Critical severity · published Apr 30, 2026
CVE-2026-40685
In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an…
9.8
CVSS
0.3%
EPSS
No
On KEV
Description
In Exim before 4.99.2, when JSON lookup is enabled, an out-of-bounds heap write can occur when a JSON operator encounters malformed JSON in an untrusted header, because of an incorrect implementation of \ skipping.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 25% 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-2026-40685
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-40685
Patch
https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
Broken Link
https://exim.org/static/doc/security/CVE-2026-40685.txt
Vendor Advisory
https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
Mailing List
https://www.openwall.com/lists/oss-security/2026/04/30/21
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