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CVE-2026-39304 is a denial-of-service vulnerability in Apache ActiveMQ affecting the Client, Broker, All, and Apache ActiveMQ distributions. The flaw is in the NIO SSL transport's handling of TLSv1.3 handshake KeyUpdate messages. A client can rapidly trigger KeyUpdate events, and the vulnerable broker does not correctly process them, causing memory exhaustion in the SSL engine and ultimately an out-of-memory condition. Apache also noted related broken handling for pre-TLSv1.3 renegotiation paths such as TLSv1.2; those cases can cause connections to hang but do not produce the same out-of-memory condition. Affected versions are ActiveMQ 5.x before 5.19.4 and 6.x from 6.0.0 before 6.2.4.
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What an attacker gets, and what they’ve been doing with it.
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6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
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Every observed campaign linking this CVE to a named adversary.
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Cross-references every affected SKU, including bundled OEM variants.
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