CVE-2026-68118: Linux

High severity, CVSS 8.2. EPSS: 0.6% chance of exploitation in the next 30 days.

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.

Affected products

• Linux Linux: from 3.0.58, before 3.1 (fixed in 3.1); from 3.2.37, before 3.3 (fixed in 3.3); from 3.4.25, before 3.5 (fixed in 3.5); from 3.6, before 6.6.153 (fixed in 6.6.153); from 6.7, before 6.12.105 (fixed in 6.12.105); from 6.13, before 6.18.42 (fixed in 6.18.42); …

Published 2026-08-10. Last modified 2026-08-23.