Home / mailings [USN-8946-1] Unbound vulnerabilities
Posted on 21 October 2026
Ubuntu Security==========================================================================Ubuntu Security Notice USN-8946-1
October 21, 2026
unbound vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:
- Ubuntu 26.04 LTS
- Ubuntu 24.04 LTS
- Ubuntu 22.04 LTS
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS
Summary:
Several security issues were fixed in Unbound.
Software Description:
- unbound: validating, recursive, caching DNS resolver
Details:
It was discovered that Unbound incorrectly handled certain TCP connections.
A remote attacker could possibly use this issue to cause Unbound to consume
resources, leading to a denial of service. This issue only affected Ubuntu
26.04 LTS, Ubuntu 24.04 LTS, Ubuntu 22.04 LTS and Ubuntu 20.04 LTS.
(CVE-2026-80225)
It was discovered that Unbound incorrectly handled certain DNS responses. A
remote attacker could possibly use this issue to crash Unbound, resulting
in a denial of service. (CVE-2026-81634)
It was discovered that Unbound incorrectly handled certain DNS responses
during DNSSEC validation. A remote attacker could possibly use this issue
to cause Unbound to consume resources, leading to a denial of service.
(CVE-2026-85501)
It was discovered that Unbound incorrectly handled outgoing network ports.
A remote attacker could possibly use this issue to crash Unbound, resulting
in a denial of service. (CVE-2026-50252)
It was discovered that Unbound incorrectly handled certain DNSCrypt
packets. A remote attacker could possibly use this issue to crash Unbound,
resulting in a denial of service. This issue only affected Ubuntu 26.04
LTS, Ubuntu 24.04 LTS, Ubuntu 22.04 LTS, Ubuntu 20.04 LTS and Ubuntu 18.04
LTS. (CVE-2026-40691)
It was discovered that Unbound incorrectly handled certain cached DNS
responses. A remote attacker could possibly use this issue to poison
Unbound's cache. This issue only affected Ubuntu 26.04 LTS, Ubuntu 24.04
LTS, Ubuntu 22.04 LTS and Ubuntu 20.04 LTS. (CVE-2026-44690)
It was discovered that Unbound incorrectly handled certain DNS-over-QUIC
connections. A remote attacker could possibly use this issue to cause
Unbound to consume resources, leading to a denial of service. This issue
only affected Ubuntu 26.04 LTS. (CVE-2026-32665)
It was discovered that Unbound incorrectly handled certain EDNS options. A
remote attacker could possibly use this issue to crash Unbound, resulting
in a denial of service. This issue only affected Ubuntu 26.04 LTS.
(CVE-2026-55973)
Elias Heftrig, Haya Schulmann, Niklas Vogel, and Michael Waidner discovered
that Unbound incorrectly handled validating DNSSEC messages. A remote
attacker could possibly use this issue to cause Unbound to consume
resources, leading to a denial of service. This issue only affected Ubuntu
18.04 LTS, Ubuntu 16.04 LTS and Ubuntu 14.04 LTS. (CVE-2023-50387)
It was discovered that Unbound incorrectly handled preparing an NSEC3
closest encloser proof. A remote attacker could possibly use this issue to
cause Unbound to consume resources, leading to a denial of service. This
issue only affected Ubuntu 18.04 LTS, Ubuntu 16.04 LTS and Ubuntu 14.04
LTS. (CVE-2023-50868)
Update instructions:
The problem can be corrected by updating your system to the following
package versions:
Ubuntu 26.04 LTS
libunbound8 1.24.2-1ubuntu2.4
unbound 1.24.2-1ubuntu2.4
Ubuntu 24.04 LTS
libunbound8 1.19.2-1ubuntu3.12
unbound 1.19.2-1ubuntu3.12
Ubuntu 22.04 LTS
libunbound8 1.13.1-1ubuntu5.17
unbound 1.13.1-1ubuntu5.17
Ubuntu 20.04 LTS
libunbound8 1.9.4-2ubuntu1.11+esm3
Available with Ubuntu Pro
unbound 1.9.4-2ubuntu1.11+esm3
Available with Ubuntu Pro
Ubuntu 18.04 LTS
libunbound2 1.6.7-1ubuntu2.6+esm6
Available with Ubuntu Pro
unbound 1.6.7-1ubuntu2.6+esm6
Available with Ubuntu Pro
Ubuntu 16.04 LTS
libunbound2 1.5.8-1ubuntu1.1+esm5
Available with Ubuntu Pro
unbound 1.5.8-1ubuntu1.1+esm5
Available with Ubuntu Pro
Ubuntu 14.04 LTS
libunbound2 1.4.22-1ubuntu4.14.04.3+esm5
Available with Ubuntu Pro
unbound 1.4.22-1ubuntu4.14.04.3+esm5
Available with Ubuntu Pro
In general, a standard system update will make all the necessary changes.
References:
https://ubuntu.com/security/notices/USN-8946-1
CVE-2023-50387, CVE-2023-50868, CVE-2026-32665, CVE-2026-40691,
CVE-2026-44690, CVE-2026-50252, CVE-2026-55973, CVE-2026-80225,
CVE-2026-81634, CVE-2026-85501
Package Information:
https://launchpad.net/ubuntu/+source/unbound/1.24.2-1ubuntu2.4
https://launchpad.net/ubuntu/+source/unbound/1.19.2-1ubuntu3.12
https://launchpad.net/ubuntu/+source/unbound/1.13.1-1ubuntu5.17
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