What’s Vulnerable › Vulnerabilities

CVE-2026-40685

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-30 · updated 2026-06-17
• Weakness: CWE-684

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.

Affected products

• Exim: before 4.99.2 — fixed in 4.99.2

How to fix

Upgrade to a fixed version: Exim 4.99.2. Check the vendor advisory for mitigations.

References

• https://code.exim.org/exim/exim/commit/9fdc057e71b87c87a0d3d2288b2810a0efaaba57
• https://exim.org/static/doc/security/CVE-2026-40685.txt
• https://exim.org/static/doc/security/cve-2026-04.1/CVE2026-40685.assessment
• https://www.openwall.com/lists/oss-security/2026/04/30/21

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