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CVE-2026-40684 is a denial-of-service vulnerability in Exim before version 4.99.2 that affects deployments running on systems using musl libc rather than glibc. When Exim processes malformed DNS data in PTR records, an oddity related to octal printing in the musl libc environment can cause the connection instance to crash. The issue is triggered during handling of attacker-controlled or otherwise malicious PTR response data and results in abnormal termination of the affected Exim connection context.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
12 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An Exim denial-of-service vulnerability on systems using musl libc, triggered by malformed DNS PTR record data that crashes connection instances.
A denial-of-service vulnerability in Exim where malformed DNS PTR data can trigger a crash on systems using the musl C library.
A vulnerability in Exim involving processing of DNS PTR responses, with impact specifically noted for systems using musl libc.
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.