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CVE-2025-40186 is a TCP Fast Open request-socket lifetime-management flaw in the Linux kernel. When a listening socket is closed while a TCP Fast Open connection is processed by tcp_conn_request(), the request socket may be removed first through tcp_disconnect(). tcp_conn_request() can then perform a second removal, decrementing the last request-socket reference. This produces a listener reference-count underflow and a request-socket double-free/use-after-free condition. The upstream correction removes the redundant reqsk_fastopen_remove() invocation from tcp_conn_request().
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31 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Linux kernel TCP connection-request handling flaw involving incorrect use of reqsk_fastopen_remove().
CVE-2025-40186 is listed in the advisory's CVE references, but the content provides no technical description or explicit security-fix entry for it.
A Linux kernel vulnerability referenced in the advisory, for which the supplied content provides no technical description.
Linux kernel TCP Fast Open flaw involving an unsafe reqsk_fastopen_remove() call in tcp_conn_request().
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.