Release notes

Version numbering

Version number format is major.minor.patch. Knot Resolver does not use semantic versioning even though the version number looks similar.

Leftmost number which was changed signalizes what to expect when upgrading:

Major version
  • Manual upgrade steps might be necessary, please follow instructions in Upgrading section.

  • Major releases may contain significant changes including changes to configuration format.

  • We might release a new major also when internal implementation details change significantly.

Minor version
  • Configuration stays compatible with the previous version, except for undocumented or very obscure options.

  • Upgrade should be seamless for users who use modules shipped as part of Knot Resolver distribution.

  • Incompatible changes in internal APIs are allowed in minor versions. Users who develop or use custom modules (i.e. modules not distributed together with Knot Resolver) need to double check their modules for incompatibilities. Upgrading section should contain hints for module authors.

Patch version
  • Everything should be compatible with the previous version.

  • API for modules should be stable on best effort basis, i.e. API is very unlikely to break in patch releases.

  • Custom modules might need to be recompiled, i.e. ABI compatibility is not guaranteed.

This definition is not applicable to versions older than 5.2.0.

Knot Resolver 5.x.y (202y-mm-dd)


  • update addresses of (!1478)


  • fix potential SERVFAIL deadlocks if net.ipv6 = false (#880)

Knot Resolver 5.7.0 (2023-08-22)


  • avoid excessive TCP reconnections in a few more cases (!1448) Like before, the remote server had to behave nonsensically in order to inflict this upon itself, but it might be abusable for DoS.

    We thank Ivan Jedek from OryxLabs for reporting this. CVE-2023-46317 got later assigned to this issue.


  • forwarding mode: tweak dealing with failures from forwarders, in particular prefer sending CD=0 upstream (!1392)


  • fix unusual timestamp format in debug dumps of records (!1386)

  • adjust linker options; it should help less common platforms (!1384)

  • hints module: fix names inside (!1406)

  • EDNS padding (RFC 8467) compatibility with knot-dns 3.3 libs (!1422)

Knot Resolver 5.6.0 (2023-01-26)


  • avoid excessive TCP reconnections in some cases (!1380) For example, a DNS server that just closes connections without answer could cause lots of work for the resolver (and itself, too). The number of connections could be up to around 100 per client’s query.

    We thank Xiang Li from NISL Lab, Tsinghua University, and Xuesong Bai and Qifan Zhang from DSP Lab, UCI.


  • daemon: feed server selection with more kinds of bad-answer events (!1380)

  • cache.max_ttl(): lower the default from six days to one day and apply both limits to the first uncached answer already (!1323 #127)

  • depend on jemalloc, preferably, to improve memory usage (!1353)

  • no longer accept DNS messages with trailing data (!1365)

  • policy.STUB: avoid applying aggressive DNSSEC denial proofs (!1364)

  • policy.STUB: avoid copying +dnssec flag from client to upstream (!1364)


  • policy.DEBUG_IF: don’t print client’s packet unconditionally (!1366)

Knot Resolver 5.5.3 (2022-09-21)


  • fix CPU-expensive DoS by malicious domains - CVE-2022-40188


  • fix config_tests on macOS (both HW variants)

Knot Resolver 5.5.2 (2022-08-16)


  • support libknot 3.2 (!1309)

  • priming module: hide failures from the default log level (!1310)

  • reduce memory usage in some cases (!1328)


  • daemon/http: improve URI checks to fix some proxies (#746, !1311)

  • daemon/tls: fix a double-free for some cases of policy.TLS_FORWARD (!1314)

  • hints module: improve parsing comments in hosts files (!1315)

  • renumber module: fix renumbering with name matching again (#760, !1334)

Knot Resolver 5.5.1 (2022-06-14)


  • daemon/tls: disable TLS resumption via tickets for TLS <= 1.2 (#742, !1295)

  • daemon/http: DoH now responds with proper HTTP codes (#728, !1279)

  • renumber module: allow rewriting subnet to a single IP (!1302)

  • renumber module: allow arbitrary netmask (!1306)

  • nameserver selection algorithm: improve IPv6 avoidance if broken (!1298)


  • modules/dns64: fix incorrect packet writes for cached packets (#727, !1275)

  • xdp: make it work also with libknot 3.1 (#735, !1276)

  • prefill module: fix lockup when starting multiple idle instances (!1285)

  • validator: fix some failing negative NSEC proofs (!1294, #738, #443)

Knot Resolver 5.5.0 (2022-03-15)


  • extended_errors: module for extended DNS error support, RFC8914 (!1234)

  • policy: log policy actions; useful for RPZ debugging (!1239)

  • policy: new action policy.IPTRACE for logging request origin (!1239)

  • prefill module: prepare for ZONEMD, improve performance (!1225)

  • validator: conditionally ignore SHA1 DS, as SHOULD by RFC4509 (!1251)

  • lib/resolve: use EDNS padding for outgoing TLS queries (!1254)

  • support for PROXYv2 protocol (!1238)

  • lib/resolve, policy: new NO_ANSWER flag for not responding to clients (!1257)

Incompatible changes

  • libknot >= 3.0.2 is required


  • doh2: fix CORS by adding access-control-allow-origin: * (!1246)

  • net: fix listen by interface - add interface suffix to link-local IPv6 (!1253)

  • daemon/tls: fix resumption for outgoing TLS (e.g. TLS_FORWARD) (!1261)

  • nameserver selection: fix interaction of timeouts with reboots (#722, !1269)

Knot Resolver 5.4.4 (2022-01-05)


  • fix bad zone cut update in certain cases (e.g. AWS; !1237)

Knot Resolver 5.4.3 (2021-12-01)


  • lua: add kres.parse_rdata() to parse RDATA from string to wire format (!1233)

  • lua: add for exact domain name matching (!1228)


  • policy.rpz: fix origin detection in files without $ORIGIN (!1215)

  • lua: log() works again; broken in 5.4.2 (!1223)

  • policy: correctly include EDNS0 previously omitted by some actions (!1230)

  • edns_keepalive: module is now properly loaded (!1229, thanks Josh Soref!)

Knot Resolver 5.4.2 (2021-10-13)


  • dns64 module: also map the reverse (PTR) subtree (#478, !1201)

  • dns64 module: allow disabling based on client address (#368, !1201)

  • dns64 module: allow configuring AAAA subnets not allowed in answer (!1201)

  • nameserver selection algorithm: improve IPv6 avoidance if broken (!1207)


  • lua: log() output is visible with default log level again (!1208)

  • build: fix when knot-dns headers are on non-standard location (!1210)

Knot Resolver 5.4.1 (2021-08-19)


  • docker: base image on Debian 11 (!1203)


  • fix build without doh2 support after 5.4.0 (!1197)

  • fix policy.DEBUG* logging and -V/–version after 5.4.0 (!1199)

  • doh2: ensure memory from unsent streams is freed (!1202)

Knot Resolver 5.4.0 (2021-07-29)


  • fine grained logging and syslog support (!1181)

  • expose HTTP headers for processing DoH requests (!1165)

  • improve assertion mechanism for debugging (!1146)

  • support apkg tool for packaging workflow (!1178)

  • support Knot DNS 3.1 (!1192, !1194)


  • trust_anchors.set_insecure: improve precision (#673, !1177)

  • plug memory leaks related to TCP (!1182)

  • policy.FLAGS: fix not applying properly in edge cases (!1179)

  • fix a crash with older libuv inside timer processing (!1195)

Incompatible changes

Knot Resolver 5.3.2 (2021-05-05)


  • validator: fix 5.3.1 regression on over-limit NSEC3 edge case (!1169) Assertion might be triggered by query/answer, potentially DoS. CVE-2021-40083 was later assigned.


  • cache: improve handling write errors from LMDB (!1159)

  • doh2: improve handling of stream errors (!1164)


  • dnstap module: fix repeated configuration (!1168)

  • validator: fix SERVFAIL for some rare dynamic proofs (!1166)

  • fix SIGBUS on uncommon ARM machines (unaligned access; !1167, #426)

  • cache: better resilience on abnormal termination/restarts (!1172)

  • doh2: fix memleak on stream write failures (!1161)

Knot Resolver 5.3.1 (2021-03-31)


  • policy.STUB: try to avoid TCP (compared to 5.3.0; !1155)

  • validator: downgrade NSEC3 records with too many iterations (>150; !1160)

  • additional improvements to nameserver selection algorithm (!1154, !1150)


  • dnstap module: don’t break request resolution on dnstap errors (!1147)

  • cache garbage collector: fix crashes introduced in 5.3.0 (!1153)

  • policy.TLS_FORWARD: better avoid dead addresses (#671, !1156)

Knot Resolver 5.3.0 (2021-02-25)


  • more consistency in using parent-side records for NS addresses (!1097)

  • better algorithm for choosing nameservers (!1030, !1126, !1140, !1141, !1143)

  • daf module: add daf.clear() (!1114)

  • dnstap module: more features and don’t log internal requests (!1103)

  • dnstap module: include in upstream packages and Docker image (!1110, !1118)

  • randomize record order by default, i.e. reorder_RR(true) (!1124)

  • prometheus module: transform graphite tags into prometheus labels (!1109)

  • avoid excessive logging of UDP replies with sendmmsg (!1138)


  • view: fail config if bad subnet is specified (!1112)

  • doh2: fix memory leak (!1117)

  • policy.ANSWER: minor fixes, mainly around NODATA answers (!1129)

  • http, watchdog modules: fix stability problems (!1136)

Incompatible changes

  • dnstap module: log_responses option gets nested under client; see new docs for config example (!1103)

  • libknot >= 2.9 is required

Knot Resolver 5.2.1 (2020-12-09)


  • doh2: send Cache-Control header with TTL (#617, !1095)


  • fix map() command on 32-bit platforms; regressed in 5.2.0 (!1093)

  • doh2: restrict endpoints to doh and dns-query (#636, !1104)

  • renumber: map to correct subnet when using multiple rules (!1107)

Knot Resolver 5.2.0 (2020-11-11)


  • doh2: add native C module for DNS-over-HTTPS (#600, !997)

  • xdp: add server-side XDP support for higher UDP performance (#533, !1083)

  • lower default EDNS buffer size to 1232 bytes (#538, #300, !920); see

  • net: split the EDNS buffer size into upstream and downstream (!1026)

  • lua-http doh: answer to /dns-query endpoint as well as /doh (!1069)

  • improve resiliency against UDP fragmentation attacks (disable PMTUD) (!1061)

  • ta_update: warn if there are differences between statically configured keys and upstream (#251, !1051)

  • human readable output in interactive mode was improved

  • doc: generate info page (!1079)

  • packaging: improve sysusers and tmpfiles support (!1080)


  • avoid an assert() error in stash_rrset() (!1072)

  • fix emergency cache locking bug introduced in 5.1.3 (!1078)

  • migrate map() command to control sockets; fix systemd integration (!1000)

  • fix crash when sending back errors over control socket (!1000)

  • fix SERVFAIL while processing forwarded CNAME to a sibling zone (#614, !1070)

Incompatible changes

Knot Resolver 5.1.3 (2020-09-08)


  • capabilities are no longer constrained when running as root (!1012)

  • cache: add percentage usage to cache.stats() (#580, !1025)

  • cache: add number of cache entries to cache.stats() (#510, !1028)

  • aarch64 support again, as some systems still didn’t work (!1033)

  • support building against Knot DNS 3.0 (!1053)


  • tls: fix compilation to support net.tls_sticket_secret() (!1021)

  • validator: ignore bogus RRSIGs present in insecure domains (!1022, #587)

  • build if libsystemd version isn’t detected as integer (#592, !1029)

  • validator: more robust reaction on missing RRSIGs (#390, !1020)

  • ta_update module: fix broken RFC5011 rollover (!1035)

  • garbage collector: avoid keeping multiple copies of cache (!1042)

Knot Resolver 5.1.2 (2020-07-01)


  • hints module: NODATA answers also for non-address queries (!1005)

  • tls: send alert to peer if handshake fails (!1007)

  • cache: fix interaction between LMDB locks and preallocation (!1013)

  • cache garbage collector: fix flushing of messages to logs (!1009)

  • cache garbage collector: fix insufficient GC on 32-bit systems (!1009)

  • graphite module: do not block resolver on TCP failures (!1014)

  • policy.rpz various fixes (!1016): $ORIGIN issues, precision of warnings, allow answering with multi-RR sets

Knot Resolver 5.1.1 (2020-05-19)


  • fix CVE-2020-12667: mitigation for NXNSAttack DNS protocol vulnerability


  • control sockets: recognize newline as command boundary

Knot Resolver 5.1.0 (2020-04-29)


  • cache garbage collector: reduce filesystem operations when idle (!946)

  • policy.DEBUG_ALWAYS and policy.DEBUG_IF for limited verbose logging (!957)

  • daemon: improve TCP query latency under heavy TCP load (!968)

  • add policy.ANSWER action (!964, #192)

  • policy.rpz support fake A/AAAA (!964, #194)


  • cache: missing filesystem support for pre-allocation is no longer fatal (#549)

  • lua: policy.rpz() no longer watches the file when watch is set to false (!954)

  • fix a strict aliasing problem that might’ve lead to “miscompilation” (!962)

  • fix handling of DNAMEs, especially signed ones (#234, !965)

  • lua resolve(): correctly include EDNS0 in the virtual packet (!963) Custom modules might have been confused by that.

  • do not leak bogus data into SERVFAIL answers (#396)

  • improve random Lua number generator initialization (!979)

  • cache: fix CNAME caching when validation is disabled (#472, !974)

  • cache: fix CNAME caching in policy.STUB mode (!974)

  • prefill: fix crash caused by race condition with resolver startup (!983)

  • webmgmt: use javascript scheme detection for websockets’ protocol (#546)

  • daf module: fix del(), deny(), drop(), tc(), pass() functions (#553, !966)

  • policy and daf modules: expose initial query when evaluating postrules (#556)

  • cache: fix some cases of caching answers over 4 KiB (!976)

  • docs: support sphinx 3.0.0+ (!978)

Incompatible changes

Knot Resolver 5.0.1 (2020-02-05)


  • systemd: use correct cache location for garbage collector (#543)


  • cache: add cache.fssize() lua function to configure entire free disk space on dedicated cache partition (#524, !932)

Knot Resolver 5.0.0 (2020-01-27)

Incompatible changes


  • logging: control-socket commands don’t log unless –verbose (#528)

  • use SO_REUSEPORT_LB if available (FreeBSD 12.0+)

  • lua: remove dependency on lua-socket and lua-sec, used lua-http and cqueues (#512, #521, !894)

  • lua: remove dependency on lua-filesystem (#520, !912)

  • net.listen(): allow binding to non-local address with freebind option (!898)

  • cache: pre-allocate the file to avoid SIGBUS later (not macOS; !917, #525)

  • lua: be stricter around nonsense returned from modules (!901)

  • user documentation was reorganized and extended (!900, !867)

  • multiple config files can be used with –config/-c option (!909)

  • lua: stop trying to tweak lua’s GC (!201)

  • systemd: add SYSTEMD_INSTANCE env variable to identify different instances (!906)


  • correctly use EDNS(0) padding in failed answers (!921)

  • policy and daf modules: fix postrules and reroute rules (!901)

  • renumber module: don’t accidentally zero-out request’s .state (!901)

Knot Resolver 4.3.0 (2019-12-04)

Security - CVE-2019-19331

  • fix speed of processing large RRsets (DoS, #518)

  • improve CNAME chain length accounting (DoS, !899)


  • http module: use SO_REUSEPORT (!879)

  • systemd: kresd@.service now properly starts after network interfaces have been configured with IP addresses after reboot (!884)

  • sendmmsg: improve reliability (!704)

  • cache: fix crash on insertion via lua for NS and CNAME (!889)

  • rpm package: move root.keys to /var/lib/knot-resolver (#513, !888)


  • increase file-descriptor count limit to maximum allowed value (hard limit; !876)

  • watchdog module: support testing a DNS query (and switch C -> lua; !878, !881)

  • performance: use sendmmsg syscall towards clients by default (!877)

  • performance: avoid excessive getsockname() syscalls (!854)

  • performance: lua-related improvements (!874)

  • daemon now attempts to drop all capabilities (!896)

  • reduce CNAME chain length limit - now <= 12 (!899)

Knot Resolver 4.2.2 (2019-10-07)


  • lua bindings: fix a 4.2.1 regression on 32-bit systems (#514) which also fixes libknot 2.9 support on all systems

Knot Resolver 4.2.1 (2019-09-26)


  • rebinding module: fix handling some requests, respect ALLOW_LOCAL flag

  • fix incorrect SERVFAIL on cached bogus answer for +cd request (!860) (regression since 4.1.0 release, in less common cases)

  • prefill module: allow a different module-loading style (#506)

  • validation: trim TTLs by RRSIG’s expiration and original TTL (#319, #504)

  • NS choice algorithm: fix a regression since 4.0.0 (#497, !868)

  • policy: special domains and local. get NXDOMAIN (!855)


  • add compatibility with (future) libknot 2.9

Knot Resolver 4.2.0 (2019-08-05)


  • queries without RD bit set are REFUSED by default (!838)

  • support forwarding to multiple targets (!825)


  • tls_client: fix issue with TLS session resumption (#489)

  • rebinding module: fix another false-positive assertion case (!851)

Module API changes

  • kr_request::add_selected is now really put into answer, instead of the “duplicate” ::additional field (#490)

Knot Resolver 4.1.0 (2019-07-10)


  • fix CVE-2019-10190: do not pass bogus negative answer to client (!827)

  • fix CVE-2019-10191: do not cache negative answer with forged QNAME+QTYPE (!839)


  • new cache garbage collector is available and enabled by default (#257) This improves cache efficiency on big installations.

  • DNS-over-HTTPS: unknown HTTP parameters are ignored to improve compatibility with non-standard clients (!832)

  • DNS-over-HTTPS: answers include access-control-allow-origin: * (!823) which allows JavaScript to use DoH endpoint.

  • http module: support named AF_UNIX stream sockets (again)

  • aggressive caching is disabled on minimal NSEC* ranges (!826) This improves cache effectivity with DNSSEC black lies and also accidentally works around bug in proofs-of-nonexistence from F5 BIG-IP load-balancers.

  • aarch64 support, even kernels with ARM64_VA_BITS >= 48 (#216, !797) This is done by working around a LuaJIT incompatibility. Please report bugs.

  • lua tables for C modules are more strict by default, e.g. will throw an error instead of returning nil (!797)

  • systemd: basic watchdog is now available and enabled by default (#275)


  • TCP to upstream: fix unlikely case of sending out wrong message length (!816)

  • http module: fix problems around maintenance of ephemeral certs (!819)

  • http module: also send intermediate TLS certificate to clients, if available and luaossl >= 20181207 (!819)

  • send EDNS with SERVFAILs, e.g. on validation failures (#180, !827)

  • prefill module: avoid crash on empty zone file (#474, !840)

  • rebinding module: avoid excessive iteration on blocked attempts (!842)

  • rebinding module: fix crash caused by race condition (!842)

  • rebinding module: log each blocked query only in verbose mode (!842)

  • cache: automatically clear stale reader locks (!844)

Module API changes

  • lua modules may omit casting parameters of layer functions (!797)

Knot Resolver 4.0.0 (2019-04-18)

Incompatible changes

  • see upgrading guide:

  • configuration: trust_anchors aliases .file, .config() and .negative were removed (!788)

  • configuration: trust_anchors.keyfile_default is no longer accessible (!788)

  • daemon: -k/–keyfile and -K/–keyfile-ro options were removed

  • meson build system is now used for builds (!771)

  • build with embedded LMBD is no longer supported

  • default modules dir location has changed

  • DNSSEC is enabled by default

  • upstream packages for Debian now require systemd

  • libknot >= 2.8 is required

  • net.list() output format changed (#448)

  • net.listen() reports error when address-port pair is in use

  • bind to DNS-over-TLS port by default (!792)

  • stop versioning libkres library

  • default port for web management and APIs changed to 8453


  • policy.TLS_FORWARD: if hostname is configured, send it on wire (!762)

  • hints module: allow configuring the TTL and change default from 0 to 5s

  • policy module: policy.rpz() will watch the file for changes by default

  • packaging: lua cqueues added to default dependencies where available

  • systemd: service is no longer auto-restarted on configuration errors

  • always send DO+CD flags upstream, even in insecure zones (#153)

  • cache.stats() output is completely new; see docs (!775)

  • improve usability of table_print() (!790, !801)

  • add DNS-over-HTTPS support (#280)

  • docker image supports and exposes DNS-over-HTTPS


  • predict module: load stats module if config didn’t specify period (!755)

  • trust_anchors: don’t do 5011-style updates on anchors from files that were loaded as unmanaged trust anchors (!753)

  • trust_anchors.add(): include these TAs in .summary() (!753)

  • policy module: support ‘#’ for separating port numbers, for consistency

  • fix startup on macOS+BSD when </dev/null and cqueues installed

  • policy.RPZ: log problems from zone-file level of parser as well (#453)

  • fix flushing of messages to logs in some cases (notably systemd) (!781)

  • fix fallback when SERVFAIL or REFUSED is received from upstream (!784)

  • fix crash when dealing with unknown TA key algorithm (#449)

  • go insecure due to algorithm support even if DNSKEY is NODATA (!798)

  • fix mac addresses in the output of net.interfaces() command (!804)

  • http module: fix too early renewal of ephemeral certificates (!808)

Module API changes

  • kr_straddr_split() changed API a bit (compiler will catch that)

  • C modules defining *_layer or *_props symbols need to change a bit See the upgrading guide for details. It’s detected on module load.

Knot Resolver 3.2.1 (2019-01-10)


  • trust_anchors: respect validity time range during TA bootstrap (!748)

  • fix TLS rehandshake handling (!739)

  • make TLS_FORWARD compatible with GnuTLS 3.3 (!741)

  • special thanks to Grigorii Demidov for his long-term work on Knot Resolver!


  • improve handling of timed out outgoing TCP connections (!734)

  • trust_anchors: check syntax of public keys in DNSKEY RRs (!748)

  • validator: clarify message about bogus non-authoritative data (!735)

  • dnssec validation failures contain more verbose reasoning (!735)

  • new function trust_anchors.summary() describes state of DNSSEC TAs (!737), and logs new state of trust anchors after start up and automatic changes

  • trust anchors: refuse revoked DNSKEY even if specified explicitly, and downgrade missing the SEP bit to a warning

Knot Resolver 3.2.0 (2018-12-17)

New features

  • module edns_keepalive to implement server side of RFC 7828 (#408)

  • module nsid to implement server side of RFC 5001 (#289)

  • module bogus_log provides .frequent() table (!629, credit Ulrich Wisser)

  • module stats collects flags from answer messages (!629, credit Ulrich Wisser)

  • module view supports multiple rules with identical address/TSIG specification and keeps trying rules until a “non-chain” action is executed (!678)

  • module experimental_dot_auth implements an DNS-over-TLS to auth protocol (!711, credit Manu Bretelle)

  • net.bpf bindings allow advanced users to use eBPF socket filters


  • http module: only run prometheus in parent process if using –forks=N, as the submodule collects metrics from all sub-processes as well.

  • TLS fixes for corner cases (!700, !714, !716, !721, !728)

  • fix build with -DNOVERBOSELOG (#424)

  • policy.{FORWARD,TLS_FORWARD,STUB}: respect net.ipv{4,6} setting (!710)

  • avoid SERVFAILs due to certain kind of NS dependency cycles, again (#374) this time seen as ‘circular dependency’ in verbose logs

  • policy and view modules do not overwrite result finished requests (!678)


  • Dockerfile: rework, basing on Debian instead of Alpine

  • policy.{FORWARD,TLS_FORWARD,STUB}: give advantage to IPv6 when choosing whom to ask, just as for iteration

  • use pseudo-randomness from gnutls instead of internal ISAAC (#233)

  • tune the way we deal with non-responsive servers (!716, !723)

  • documentation clarifies interaction between policy and view modules (!678, !730)

Module API changes

  • new layer is added: answer_finalize

  • kr_request keeps ::qsource.packet beyond the begin layer

  • kr_request::qsource.tcp renamed to ::qsource.flags.tcp

  • kr_request::has_tls renamed to ::qsource.flags.tls

  • kr_zonecut_add(), kr_zonecut_del() and kr_nsrep_sort() changed parameters slightly

Knot Resolver 3.1.0 (2018-11-02)

Incompatible changes

  • hints.use_nodata(true) by default; that’s what most users want

  • libknot >= 2.7.2 is required


  • cache: handle out-of-space SIGBUS slightly better (#197)

  • daemon: improve TCP timeout handling (!686)


  • cache.clear(‘name’): fix some edge cases in API (#401)

  • fix error handling from TLS writes (!669)

  • avoid SERVFAILs due to certain kind of NS dependency cycles (#374)

Knot Resolver 3.0.0 (2018-08-20)

Incompatible changes

  • cache: fail lua operations if cache isn’t open yet (!639) By default cache is opened after reading the configuration, and older versions were silently ignoring cache operations. Valid configuration must open cache using or cache.size = before executing cache operations like cache.clear().

  • libknot >= 2.7.1 is required, which brings also larger API changes

  • in case you wrote custom Lua modules, please consult

  • in case you wrote custom C modules, please see compile against Knot DNS 2.7 and adjust your module according to messages from C compiler

  • DNS cookie module (RFC 7873) is not available in this release, it will be later reworked to reflect development in IEFT dnsop working group

  • version module was permanently removed because it was not really used by users; if you want to receive notifications about new releases please subscribe to


  • fix multi-process race condition in trust anchor maintenance (!643)

  • ta_sentinel: also consider static trust anchors not managed via RFC 5011


  • reorder_RR() implementation is brought back

  • bring in performance improvements provided by libknot 2.7

  • cache.clear() has a new, more powerful API

  • cache documentation was improved

  • old name “Knot DNS Resolver” is replaced by unambiguous “Knot Resolver” to prevent confusion with “Knot DNS” authoritative server

Knot Resolver 2.4.1 (2018-08-02)


  • fix CVE-2018-10920: Improper input validation bug in DNS resolver component (security!7, security!9)


  • cache: fix TTL overflow in packet due to min_ttl (#388, security!8)

  • TLS session resumption: avoid bad scheduling of rotation (#385)

  • HTTP module: fix a regression in 2.4.0 which broke custom certs (!632)

  • cache: NSEC3 negative cache even without NS record (#384) This fixes lower hit rate in NSEC3 zones (since 2.4.0).

  • minor TCP and TLS fixes (!623, !624, !626)

Knot Resolver 2.4.0 (2018-07-03)

Incompatible changes

  • minimal libknot version is now 2.6.7 to pull in latest fixes (#366)


  • fix a rare case of zones incorrectly downgraded to insecure status (!576)

New features

  • TLS session resumption (RFC 5077), both server and client (!585, #105) (disabled when compiling with gnutls < 3.5)

  • TLS_FORWARD policy uses system CA certificate store by default (!568)

  • aggressive caching for NSEC3 zones (!600)

  • optional protection from DNS Rebinding attack (module rebinding, !608)

  • module bogus_log to log DNSSEC bogus queries without verbose logging (!613)


  • prefill: fix ability to read certificate bundle (!578)

  • avoid turning off qname minimization in some cases, e.g. (#339)

  • fix validation of explicit wildcard queries (#274)

  • dns64 module: more properties from the RFC implemented (incl. bug #375)


  • systemd: multiple enabled kresd instances can now be started using

  • ta_sentinel: switch to version 14 of the RFC draft (!596)

  • support for glibc systems with a non-Linux kernel (!588)

  • support per-request variables for Lua modules (!533)

  • support custom HTTP endpoints for Lua modules (!527)

Knot Resolver 2.3.0 (2018-04-23)


  • fix CVE-2018-1110: denial of service triggered by malformed DNS messages (!550, !558, security!2, security!4)

  • increase resilience against slow lorris attack (security!5)

New features

  • new policy.REFUSE to reply REFUSED to clients


  • validation: fix SERVFAIL in case of CNAME to NXDOMAIN in a single zone (!538)

  • validation: fix SERVFAIL for DS . query (!544)

  • lib/resolve: don’t send unnecessary queries to parent zone (!513)

  • iterate: fix validation for zones where parent and child share NS (!543)

  • TLS: improve error handling and documentation (!536, !555, !559)


  • prefill: new module to periodically import root zone into cache (replacement for RFC 7706, !511)

  • network_listen_fd: always create end point for supervisor supplied file descriptor

  • use CPPFLAGS build environment variable if set (!547)

Knot Resolver 2.2.0 (2018-03-28)

New features

  • cache server unavailability to prevent flooding unreachable servers (Please note that caching algorithm needs further optimization and will change in further versions but we need to gather operational experience first.)


  • don’t magically -D_FORTIFY_SOURCE=2 in some cases

  • allow large responses for outbound over TCP

  • fix crash with RR sets with over 255 records

Knot Resolver 2.1.1 (2018-02-23)


  • when iterating, avoid unnecessary queries for NS in insecure parent. This problem worsened in 2.0.0. (#246)

  • prevent UDP packet leaks when using TLS forwarding

  • fix the hints module also on some other systems, e.g. Gentoo.

Knot Resolver 2.1.0 (2018-02-16)

Incompatible changes

  • stats: remove tracking of expiring records (predict uses another way)

  • systemd: re-use a single kresd.socket and kresd-tls.socket

  • ta_sentinel: implement protocol draft-ietf-dnsop-kskroll-sentinel-01 (our draft-ietf-dnsop-kskroll-sentinel-00 implementation had inverted logic)

  • libknot: require version 2.6.4 or newer to get bugfixes for DNS-over-TLS


  • detect_time_jump module: don’t clear cache on suspend-resume (#284)

  • stats module: fix stats.list() returning nothing, regressed in 2.0.0

  • policy.TLS_FORWARD: refusal when configuring with multiple IPs (#306)

  • cache: fix broken refresh of insecure records that were about to expire

  • fix the hints module on some systems, e.g. Fedora (came back on 2.0.0)

  • build with older gnutls (conditionally disable features)

  • fix the predict module to work with insecure records & cleanup code

Knot Resolver 2.0.0 (2018-01-31)

Incompatible changes

  • systemd: change unit files to allow running multiple instances, deployments with single instance now must use kresd@1.service instead of kresd.service; see kresd.systemd(7) for details

  • systemd: the directory for cache is now /var/cache/knot-resolver

  • unify default directory and user to knot-resolver

  • directory with trust anchor file specified by -k option must be writeable

  • policy module is now loaded by default to enforce RFC 6761; see documentation for policy.PASS if you use locally-served DNS zones

  • drop support for alternative cache backends memcached, redis, and for Lua bindings for some specific cache operations

  • REORDER_RR option is not implemented (temporarily)

New features

  • aggressive caching of validated records (RFC 8198) for NSEC zones; thanks to ICANN for sponsoring this work.

  • forwarding over TLS, authenticated by SPKI pin or certificate. policy.TLS_FORWARD pipelines queries out-of-order over shared TLS connection Beware: Some resolvers do not support out-of-order query processing. TLS forwarding to such resolvers will lead to slower resolution or failures.

  • trust anchors: you may specify a read-only file via -K or –keyfile-ro

  • trust anchors: at build-time you may set KEYFILE_DEFAULT (read-only)

  • ta_sentinel module implements draft ietf-dnsop-kskroll-sentinel-00, enabled by default

  • serve_stale module is prototype, subject to change

  • extended API for Lua modules


  • fix build on osx - regressed in 1.5.3 (different linker option name)

Knot Resolver 1.5.3 (2018-01-23)


  • fix the hints module on some systems, e.g. Fedora. Symptom: undefined symbol: engine_hint_root_file

Knot Resolver 1.5.2 (2018-01-22)


  • fix CVE-2018-1000002: insufficient DNSSEC validation, allowing attackers to deny existence of some data by forging packets. Some combinations pointed out in RFC 6840 sections 4.1 and 4.3 were not taken into account.


  • memcached: fix fallout from module rename in 1.5.1

Knot Resolver 1.5.1 (2017-12-12)

Incompatible changes

  • script was removed, please migrate to a real process manager

  • module ketcd was renamed to etcd for consistency

  • module kmemcached was renamed to memcached for consistency


  • fix SIGPIPE crashes (#271)

  • tests: work around out-of-space for platforms with larger memory pages

  • lua: fix mistakes in bindings affecting 1.4.0 and 1.5.0 (and 1.99.1-alpha), potentially causing problems in dns64 and workarounds modules

  • predict module: various fixes (!399)


  • add priming module to implement RFC 8109, enabled by default (#220)

  • add modules helping with system time problems, enabled by default; for details see documentation of detect_time_skew and detect_time_jump

Knot Resolver 1.5.0 (2017-11-02)


  • fix loading modules on Darwin


  • new module ta_signal_query supporting Signaling Trust Anchor Knowledge using Keytag Query (RFC 8145 section 5); it is enabled by default

  • attempt validation for more records but require it for fewer of them (e.g. avoids SERVFAIL when server adds extra records but omits RRSIGs)

Knot Resolver 1.99.1-alpha (2017-10-26)

This is an experimental release meant for testing aggressive caching. It contains some regressions and might (theoretically) be even vulnerable. The current focus is to minimize queries into the root zone.


  • negative answers from validated NSEC (NXDOMAIN, NODATA)

  • verbose log is very chatty around cache operations (maybe too much)


  • dropped support for alternative cache backends and for some specific cache operations

  • caching doesn’t yet work for various cases:
    • negative answers without NSEC (i.e. with NSEC3 or insecure)
      • +cd queries (needs other internal changes)

      • positive wildcard answers

  • spurious SERVFAIL on specific combinations of cached records, printing:

    <= bad keys, broken trust chain

  • make check

  • a few Deckard tests are broken, probably due to some problems above

  • also unknown ones?

Knot Resolver 1.4.0 (2017-09-22)

Incompatible changes

  • lua: query flag-sets are no longer represented as plain integers. kres.query.* no longer works, and kr_query_t lost trivial methods ‘hasflag’ and ‘resolved’. You can instead write code like qry.flags.NO_0X20 = true.


  • fix exiting one of multiple forks (#150)

  • cache: change the way of using LMDB transactions. That in particular fixes some cases of using too much space with multiple kresd forks (#240).


  • policy.suffix: update the aho-corasick code (#200)

  • root hints are now loaded from a zonefile; exposed as hints.root_file(). You can override the path by defining ROOTHINTS during compilation.

  • policy.FORWARD: work around resolvers adding unsigned NS records (#248)

  • reduce unneeded records previously put into authority in wildcarded answers

Knot Resolver 1.3.3 (2017-08-09)


  • Fix a critical DNSSEC flaw. Signatures might be accepted as valid even if the signed data was not in bailiwick of the DNSKEY used to sign it, assuming the trust chain to that DNSKEY was valid.


  • iterate: skip RRSIGs with bad label count instead of immediate SERVFAIL

  • utils: fix possible incorrect seeding of the random generator

  • modules/http: fix compatibility with the Prometheus text format


  • policy: implement remaining special-use domain names from RFC6761 (#205), and make these rules apply only if no other non-chain rule applies

Knot Resolver 1.3.2 (2017-07-28)


  • fix possible opportunities to use insecure data from cache as keys for validation


  • daemon: check existence of config file even if rundir isn’t specified

  • policy.FORWARD and STUB: use RTT tracking to choose servers (#125, #208)

  • dns64: fix CNAME problems (#203) It still won’t work with policy.STUB.

  • hints: better interpretation of hosts-like files (#204)

    also, error out if a bad entry is encountered in the file

  • dnssec: handle unknown DNSKEY/DS algorithms (#210)

  • predict: fix the module, broken since 1.2.0 (#154)


  • embedded LMDB fallback: update 0.9.18 -> 0.9.21

Knot Resolver 1.3.1 (2017-06-23)


  • modules/http: fix finding the static files (bug from 1.3.0)

  • policy.FORWARD: fix some cases of CNAMEs obstructing search for zone cuts

Knot Resolver 1.3.0 (2017-06-13)


  • Refactor handling of AD flag and security status of resource records. In some cases it was possible for secure domains to get cached as insecure, even for a TLD, leading to disabled validation. It also fixes answering with non-authoritative data about nameservers.


  • major feature: support for forwarding with validation (#112). The old policy.FORWARD action now does that; the previous non-validating mode is still available as policy.STUB except that also uses caching (#122).

  • command line: specify ports via @ but still support # for compatibility

  • policy: recognize as local addresses

  • layer/iterate: do retry repeatedly if REFUSED, as we can’t yet easily retry with other NSs while avoiding retrying with those who REFUSED

  • modules: allow changing the directory where modules are found, and do not search the default library path anymore.


  • validate: fix insufficient caching for some cases (relatively rare)

  • avoid putting “duplicate” record-sets into the answer (#198)

Knot Resolver 1.2.6 (2017-04-24)


  • dnssec: don’t set AD flag for NODATA answers if wildcard non-existence is not guaranteed due to opt-out in NSEC3


  • layer/iterate: don’t retry repeatedly if REFUSED


  • lib/nsrep: revert some changes to NS reputation tracking that caused severe problems to some users of 1.2.5 (#178 and #179)

  • dnssec: fix verification of wildcarded non-singleton RRsets

  • dnssec: allow wildcards located directly under the root

  • layer/rrcache: avoid putting answer records into queries in some cases

Knot Resolver 1.2.5 (2017-04-05)


  • layer/validate: clear AD if closest encloser proof has opt-outed NSEC3 (#169)

  • layer/validate: check if NSEC3 records in wildcard expansion proof has an opt-out

  • dnssec/nsec: missed wildcard no-data answers validation has been implemented


  • modules/dnstap: a DNSTAP support module (Contributed by Vicky Shrestha)

  • modules/workarounds: a module adding workarounds for known DNS protocol violators

  • layer/iterate: fix logging of glue addresses

  • kr_bitcmp: allow bits=0 and consequently matches in view and renumber modules.

  • modules/padding: Improve default padding of responses (Contributed by Daniel Kahn Gillmor)

  • New kresc client utility (experimental; don’t rely on the API yet)


  • trust anchors: Improve trust anchors storage format (#167)

  • trust anchors: support non-root TAs, one domain per file

  • policy.DENY: set AA flag and clear AD flag

  • lib/resolve: avoid unnecessary DS queries

  • lib/nsrep: don’t treat servers with NOIP4 + NOIP6 flags as timed out

  • layer/iterate: During packet classification (answer vs. referral) don’t analyze AUTHORITY section in authoritative answer if ANSWER section contains records that have been requested

Knot Resolver 1.2.4 (2017-03-09)


  • Knot Resolver 1.2.0 and higher could return AD flag for insecure answer if the daemon received answer with invalid RRSIG several times in a row.


  • modules/policy: allow QTRACE policy to be chained with other policies

  • hints.add_hosts(path): a new property

  • module: document the API and simplify the code

  • policy.MIRROR: support IPv6 link-local addresses

  • policy.FORWARD: support IPv6 link-local addresses

  • add net.outgoing_{v4,v6} to allow specifying address to use for connections


  • layer/iterate: some improvements in cname chain unrolling

  • layer/validate: fix duplicate records in AUTHORITY section in case of WC expansion proof

  • lua: do not truncate cache size to unsigned

  • forwarding mode: correctly forward +cd flag

  • fix a potential memory leak

  • don’t treat answers that contain DS non-existence proof as insecure

  • don’t store NSEC3 and their signatures in the cache

  • layer/iterate: when processing delegations, check if qname is at or below new authority

Knot Resolver 1.2.3 (2017-02-23)


  • Disable storing GLUE records into the cache even in the (non-default) QUERY_PERMISSIVE mode

  • iterate: skip answer RRs that don’t match the query

  • layer/iterate: some additional processing for referrals

  • lib/resolve: zonecut fetching error was fixed

Knot Resolver 1.2.2 (2017-02-10)


  • Fix -k argument processing to avoid out-of-bounds memory accesses

  • lib/resolve: fix zonecut fetching for explicit DS queries

  • hints: more NULL checks

  • Fix TA bootstrapping for multiple TAs in the IANA XML file


  • Update tests to run tests with and without QNAME minimization

Knot Resolver 1.2.1 (2017-02-01)


  • Under certain conditions, a cached negative answer from a CD query would be reused to construct response for non-CD queries, resulting in Insecure status instead of Bogus. Only 1.2.0 release was affected.


  • Update the typo in the documentation: The query trace policy is named policy.QTRACE (and not policy.TRACE)


  • lua: make the map command check its arguments

Knot Resolver 1.2.0 (2017-01-24)


  • In a policy.FORWARD() mode, the AD flag was being always set by mistake. It is now cleared, as the policy.FORWARD() doesn’t do DNSSEC validation yet.


  • The DNSSEC Validation has been refactored, fixing many resolving failures.

  • Add module version that checks for updates and CVEs periodically.

  • Support RFC7830: EDNS(0) padding in responses over TLS.

  • Support CD flag on incoming requests.

  • hints module: previously /etc/hosts was loaded by default, but not anymore. Users can now actually avoid loading any file.

  • DNS over TLS now creates ephemeral certs.

  • Configurable cache.{min,max}_ttl option, with max_ttl defaulting to 6 days.

  • Option to reorder RRs in the response.

  • New policy.QTRACE policy to print packet contents


  • Trust Anchor configuration is now more robust.

  • Correctly answer NOTIMPL for meta-types and non-IN RR classes.

  • Free TCP buffer on cancelled connection.

  • Fix crash in hints module on empty hints file, and fix non-lowercase hints.


  • It now requires knot >= 2.3.1 to link successfully.

  • The API+ABI for modules changed slightly.

  • New LRU implementation.

Knot Resolver 1.1.1 (2016-08-24)


  • Fix 0x20 randomization with retransmit

  • Fix pass-through for the stub mode

  • Fix the root hints IPv6 addresses

  • Fix dst addr for retries over TCP


  • Track RTT of all tried servers for faster retransmit

  • DAF: Allow forwarding to custom port

  • systemd: Read EnvironmentFile and user $KRESD_ARGS

  • systemd: Update systemd units to be named after daemon

Knot Resolver 1.1.0 (2016-08-12)


  • RFC7873 DNS Cookies

  • RFC7858 DNS over TLS

  • HTTP/2 web interface, RESTful API

  • Metrics exported in Prometheus

  • DNS firewall module

  • Explicit CNAME target fetching in strict mode

  • Query minimisation improvements

  • Improved integration with systemd

Knot Resolver 1.0.0 (2016-05-30)

Initial release:

  • The first initial release