[Pdns-announce] security advisory 2021-01 for PowerDNS Authoritative Server 4.5.0

[Peter van Dijk]

Hello,

today we have released PowerDNS Authoritative Server 4.5.1, fixing a
remotely triggered crash present in version 4.5.0. No other versions
are affected.

Tarballs and signatures are available at 
https://downloads.powerdns.com/releases/, and a single patch is
available at https://downloads.powerdns.com/patches/2021-01/. However,
4.5.1 contains no other changes.

Please find the full text of the advisory below.

PowerDNS Security Advisory 2021-01: Specific query crashes
Authoritative Server

-  CVE: CVE-2021-36754
-  Date: July 26th, 2021
-  Affects: PowerDNS Authoritative version 4.5.0
-  Not affected: 4.4.x and below, 4.5.1
-  Severity: High
-  Impact: Denial of service
-  Exploit: This problem can be triggered via a specific query packet
-  Risk of system compromise: None
-  Solution: Upgrade to 4.5.1, or filter queries in ``dnsdist``

PowerDNS Authoritative Server 4.5.0 (and the alpha/beta/rc1/rc2
prereleases that came before it) will crash with an uncaught out of
bounds exception if it receives a query with QTYPE 65535. The offending
code was not present in earlier versions, and they are not affected.

Users that cannot upgrade immediately, but do have dnsdist in place,
can use dnsdist to filter such queries before they do harm, with
something like ``addAction(QTypeRule(65535),
RCodeAction(DNSRCode.REFUSED))``.

When the PowerDNS Authoritative Server is run inside a supervisor like
supervisord or systemd, an uncaught exception crash will lead to an
automatic restart, limiting the impact to a somewhat degraded service.

We would like to thank Reinier Schoof and Robin Geuze of TransIP for
noticing crashes in production, immediately letting us know, and
helping us figure out what was happening.
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