Bug 2464249 (CVE-2026-40685)

Summary: CVE-2026-40685 Exim: Exim: Denial of Service due to malformed JSON processing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
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Priority: medium    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Exim. When JSON lookup is enabled, a remote attacker can send specially crafted malformed JSON in an untrusted header, leading to an out-of-bounds heap write. This issue, caused by an incorrect implementation of backslash skipping, can result in a denial of service.
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Description OSIDB Bzimport 2026-04-30 22:01:35 UTC
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.