Medium severity · published Apr 30, 2026
CVE-2026-40686
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)
5.3
CVSS
0.2%
EPSS
No
On KEV
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
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
Low
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 16% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
EX
Exim · Exim
before 4.99.2 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-40686
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40686
Patch
https://code.exim.org/exim/exim/commit/f2570bde16fb4d4a1242ff363a4c4eecf6372efc
Broken Link
https://exim.org/static/doc/security/CVE-2026-40686.txt
Vendor Advisory
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40686.assessment
Mailing List
https://www.openwall.com/lists/oss-security/2026/04/30/21
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