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CVE-2025-39955 is a flaw in Linux kernel TCP Fast Open handling. When tcp_disconnect() disconnects a server-side TCP Fast Open socket, it failed to clear the socket's fastopen_rsk request-socket state. If that socket is reused as a client before the original TCP Fast Open three-way handshake completes, stale state remains after the socket transitions from TCP_SYN_RECV to TCP_CLOSE. A subsequent retransmission-timer invocation can operate on the stale state, generate a kernel warning, and fail to retransmit the intended packet. The upstream correction invokes reqsk_fastopen_remove() from tcp_disconnect().
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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().
Linux kernel TCP flaw involving failure to clear the Fast Open request-socket pointer during tcp_disconnect().
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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.
Community discussion across Reddit, Mastodon, and other social sources.