Today we released two new versions of DNSdist, 1.9.13 and 2.0.4, fixing several security issues that have been reported to us. These security issues are medium to high severity, and we recommend upgrading quickly.
The issues fixed in these releases are:
CVE-2026-33254: An attacker can create a large number of concurrent DoQ or DoH3 connections, causing unlimited memory allocation in DNSdist and leading to a denial of service. DOQ and DoH3 are disabled by default
CVE-2026-33257: An attacker can send a web request that causes unlimited memory allocation in the internal web server, leading to a denial of service. The web server is disabled and restricted by an ACL by default
CVE-2026-33260: An attacker can send a web request that causes unlimited memory allocation in the internal web server, leading to a denial of service. The web server is disabled and restricted by an ACL by default
CVE-2026-33593: A client can trigger a divide by zero error leading to crash by sending a crafted DNSCrypt query. DNSCrypt is disabled by default
CVE-2026-33594: A client can trigger excessive memory allocation by generating a lot of queries that are routed to an overloaded DoH backend, causing queries to accumulate into a buffer that will not be released until the end of the connection. Outgoing DoH is disabled by default
CVE-2026-33595: A client can trigger excessive memory allocation by generating a lot of errors responses over a single DoQ and DoH3 connection, as some resources were not properly released until the end of the connection. DOQ and DoH3 are disabled by default
CVE-2026-33596: A client might theoretically be able to cause a mismatch between queries sent to a backend and the received responses by sending a flood of perfectly timed queries that are routed to a TCP-only or DNS over TLS backend
CVE-2026-33597: A crafted query containing an invalid DNS label can prevent the PRSD detection algorithm executed via DynBlockRulesGroup:setSuffixMatchRule or DynBlockRulesGroup:setSuffixMatchRuleFFI from being executed
CVE-2026-33598: A cached crafted response can cause an out-of-bounds read if custom Lua code calls getDomainListByAddress() or getAddressListByDomain() on a packet cache
CVE-2026-33599: A rogue backend can send a crafted SVCB response to a Discovery of Designated Resolvers request, when requested via either the autoUpgrade (Lua) option to newServer or auto_upgrade (YAML) settings. DDR upgrade is not enabled by default
CVE-2026-33602: A rogue backend can send a crafted UDP response with a query ID off by one related to the maximum configured value, triggering an out-of-bounds write leading to a denial of service
The complete list of changes can be found in the ChangeLogs (1.9.13, 2.0.4).
Please see the DNSdist website for the current documentation. The upgrade guide is also available there. The full security advisory can be found on our website as well.
Please send us all feedback and issues you might have via the mailing list, or in case of a bug, via GitHub.
The release tarballs (1.9.13, 2.0.4) and their signatures (1.9.13, 2.0.4) are available on the downloads website, and packages for several distributions are available from our repository.