CVE-2026-40686

Description

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.

CVSS Vector

References

• 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