CVE-2026-68118: tcp: challenge ACK for non-exact RST in SYN-RECEIVED
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 tcpcheckreq() 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 tcpsendchallengeack() so request sockets can share it. Use the request socket's sendack() callback and its own out-of-window ACK timestamp to send and rate-limit the response.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-68118?
The severity of CVE-2026-68118 is rated as risk level 33.
How do I fix CVE-2026-68118?
To mitigate CVE-2026-68118, you should update to the latest version of the Linux kernel that includes the fix.
What versions of the Linux kernel are affected by CVE-2026-68118?
CVE-2026-68118 affects older versions of the Linux kernel prior to the resolution published on August 10, 2026.
What is the impact of CVE-2026-68118?
CVE-2026-68118 allows an in-window RST to disrupt the SYN-RECEIVED state in TCP connections.
Is CVE-2026-68118 exploitable remotely?
Yes, CVE-2026-68118 may be exploited remotely due to its nature affecting TCP connections.