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UBUNTU SECURITY NOTICECANONICALVERIFIED

PUBLISHER UPDATE · USN-8840-1

USN-8840-1 release notes and known issues

USN-8840-1: libevent vulnerabilities

Scope: Ubuntu. This update record adds version, fix and known-issue context. Its publication date is not a lifecycle boundary.

Summary

Michał Majchrowicz and Marcin Wyczechowski discovered that libevent incorrectly handled certain DNS responses. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. (CVE-2026-63387) It was discovered that libevent incorrectly handled certain connections. A local attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS. (CVE-2026-63388)

Improvements and security content

  • Michał Majchrowicz and Marcin Wyczechowski discovered that libevent incorrectly handled certain DNS responses. A remote attacker could possibly use this issue to cause a denial of service or execute arbitrary code. (CVE-2026-63387) It was discovered that libevent incorrectly handled certain connections. A local attacker could possibly use this issue to cause a denial of service or execute arbitrary code. This issue only affected Ubuntu 18.04 LTS, Ubuntu 20.04 LTS, Ubuntu 22.04 LTS, Ubuntu 24.04 LTS, and Ubuntu 26.04 LTS. (CVE-2026-63388)

Known issues

Publisher statement

Not stated. The verified publisher record does not contain a known-issues statement.

Affected products and versions

Products

  • Ubuntu

Affected versions

  • 18.04
  • 20.04
  • 22.04
  • 24.04
  • 26.04

Fixed versions or updates

  • No fixed version is stated in this record.

Recommended action

Review the official publisher document before deployment.

Related vulnerabilities

BlackTree CVE Intelligence
CVE-2026-63387Open CVE report →CVE-2026-63388Open CVE report →

These links connect the publisher update to related Lifecycle records without treating the update publication date as an end-of-support date.

Ubuntu 24.04 LTSOpen lifecycle record →

Official publisher evidence

CANONICALVERIFIED

USN-8840-1: libevent vulnerabilities

Checked 29 Sep 2026. BlackTree preserves the last verified facts if a later source check is temporarily unavailable.

Open the official publisher source