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CVE-2025-39955 is an incomplete-cleanup flaw in the Linux kernel TCP implementation. tcp_disconnect() failed to clear tcp_sk(sk)->fastopen_rsk when a server-side TCP Fast Open (TFO) socket was disconnected and reused as a client before its original three-way handshake completed. The sequence accept(), connect(AF_UNSPEC), and connect() to a new destination can leave stale Fast Open request state after the socket transitions from TCP_SYN_RECV to TCP_CLOSE. A subsequent retransmission timer can trigger a kernel warning and fail to retransmit the intended packet.
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No public exploit code observed for this vulnerability.
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36 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An important-severity local vulnerability addressed by the TuxCare CentOS 7 CLSA-2026-1768110920 advisory. Successful exploitation requires low privileges and could result in complete confidentiality, integrity, and availability impact.
A Linux kernel TCP Fast Open state-management flaw in tcp_disconnect().
A Linux kernel TCP flaw involving failure to clear tcp_sk(sk)->fastopen_rsk during tcp_disconnect(). It is addressed by the Red Hat kernel-rt update.
Linux kernel TCP flaw involving failure to clear tcp_sk(sk)->fastopen_rsk during tcp_disconnect().
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.