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CVE-2026-40685 is a memory-safety vulnerability in Exim before version 4.99.2 affecting configurations where JSON lookup functionality is enabled and JSON operators are applied to externally supplied data in message headers. When a JSON operator processes malformed JSON from an untrusted header, an incorrect implementation of backslash escaping can cause out-of-bounds heap write behavior; available reporting also indicates associated out-of-bounds read conditions. The flaw can lead directly to heap corruption during header processing.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
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No public exploit code observed for this vulnerability.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
13 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An Exim memory corruption vulnerability involving out-of-bounds read/write conditions triggered by invalid external input processed through JSON operators.
A vulnerability in Exim related to processing JSON data that can lead to a memory-related error.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.