Out-of-bounds Read The advisory has been revoked - it doesn't affect any version of package exim4 (opens in a new tab)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-UBUNTU1804-EXIM4-16338071
- published29 May 2026
- disclosed30 Apr 2026
Introduced: 30 Apr 2026
CVE-2026-40686 (opens in a new tab)Amendment
The Ubuntu security team deemed this advisory irrelevant for Ubuntu:18.04.
NVD Description
Note: Versions mentioned in the description apply only to the upstream exim4 package and not the exim4 package as distributed by Ubuntu.
In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing characters are present (malformed UTF-8 header data). Information might be divulged within an error message produced during handling of an unrelated e-mail message.
References
- http://people.ubuntu.com/~ubuntu-security/cve/CVE-2026-40686
- https://exim.org/static/doc/security/CVE-2025-40686.txt
- https://code.exim.org/exim/exim/commit/f2570bde16fb4d4a1242ff363a4c4eecf6372efc
- https://exim.org/static/doc/security/CVE-2026-40686.txt
- https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40686.assessment
- https://www.openwall.com/lists/oss-security/2026/04/30/21