In Exim before 4.99.2, when utf8 operators are enabled, there is an out-of-bounds read if large UTF-8 trailing
Source GCVE Database
Not known to be exploited · CVSS 3.7 Low.
Data as of 27 Oct 2026, 00:35 UTC
- Affects
- Exim before 4.99.2
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:NExploitation evidence
Disclosed: evidence found.
CVE published 30 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
AI-suggested
Until an official fix is available, consider disabling UTF-8 operators if feasible to reduce exposure. Monitor vendor communications for updates and apply patches promptly once released.
Description
A vulnerability in Exim versions before 4.99.2 exists when UTF-8 operators are enabled. This flaw causes an out-of-bounds read if large malformed UTF-8 trailing characters are present in email headers. The issue may lead to information disclosure through error messages generated during the processing of unrelated emails.
References
- nvd.nist.gov/vuln/detail/CVE-2026-40686 (opens in a new tab)
- code.exim.org/exim/exim/commit/f2570bde16fb4d4a1242ff363a4c4eecf6372efc (opens in a new tab)
- exim.org/static/doc/security/CVE-2025-40686.txt (opens in a new tab)
- exim.org/static/doc/security/CVE-2026-40686.txt (opens in a new tab)
- exim.org/static/doc/security/cve-2026-04.1/CVE2026-40686.assessment (opens in a new tab)
- openwall.com/lists/oss-security/2026/04/30/21 (opens in a new tab)