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Ubuntu 22.04 LTS: Critical Cache Poisoning Issue in Unbound USN-7666-1

ubuntu
Calendar Grey July 22, 2025
Dist Ubuntu Esm H88
The security flaw in Unbound's caching mechanism may be compromised through specially designed network packets. Prompt patching advised.
The Unbound cache could be poisoned if it received specially crafted network traffic.

Summary

The Unbound cache could be poisoned if it received specially crafted

network traffic.

Software Description:

- unbound: validating, recursive, caching DNS resolver

Details:

Xiang Li discovered that Unbound incorrectly handled EDNS Client Subnet

(ECS) in certain configurations. A remote attacker could possibly use this

issue to perform a cache poisoning attack called Rebirthday Attack.

Topics%20covered

Topics Covered

security advisory DoS Ubuntu important cache poisoning unbound

Update Instructions

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 25.04
  libunbound8                     1.22.0-1ubuntu1.1
  unbound                         1.22.0-1ubuntu1.1

Ubuntu 24.04 LTS
  libunbound8                     1.19.2-1ubuntu3.5
  unbound                         1.19.2-1ubuntu3.5

Ubuntu 22.04 LTS
  libunbound8                     1.13.1-1ubuntu5.11
  unbound                         1.13.1-1ubuntu5.11

In general, a standard system update will make all the necessary changes.

References

https://ubuntu.com/security/notices/USN-7666-1

CVE-2025-5994

Severity
critical
Lowest
Low
Medium
High
Critical

Ubuntu Security Notice USN-7666-1

Topics%20covered

Topics Covered

security advisory DoS Ubuntu important cache poisoning unbound

Package Information

https://launchpad.net/ubuntu/+source/unbound/1.22.0-1ubuntu1.1
https://launchpad.net/ubuntu/+source/unbound/1.19.2-1ubuntu3.5
https://launchpad.net/ubuntu/+source/unbound/1.13.1-1ubuntu5.11

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