CVE-2026-68118

/// Technical description

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 socket's send_ack() callback and its own

out-of-window ACK timestamp to send and rate-limit the response.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References