CVE-2026-68118

In the Linux kernel, the following vulnerability has been resolved:

tcp: challenge ACK for non-exact RST in SYN-RECEIVED

The SYN-RECEIVED request-socket path in tcp_check_req() accepts an in-window RST without requiring SEG.SEQ to exactly match RCV.NXT. A non-exact RST therefore removes the request instead of eliciting a challenge ACK.

RFC 9293 section 3.10.7.4 applies the RFC 5961 reset check in SYN-RECEIVED: an exact RST resets the connection, while a non-exact in-window RST must trigger a challenge ACK and be dropped.

Apply that check before the ACK-field validation, following the RFC sequence-number, RST, then ACK processing order. Factor the per-netns challenge ACK quota out of tcp_send_challenge_ack() so request sockets can share it. Use the request sockets send_ack() callback and its own out-of-window ACK timestamp to send and rate-limit the response.

Affected Software

References

• https://git.kernel.org/stable/c/22cec809b048495310f206d9abbcdbbfbdce3ae3
• https://git.kernel.org/stable/c/234f9ffbd9b2c1b24ec67200ea3cff07401bec48
• https://git.kernel.org/stable/c/a28c4fcbf774e23b4779cae468e3497a5ad1f4a1