CVE-2026-98255

tcp: exclude old ACKs from tcp fast path

State: Published
Severity: Not scored
Published: Oct 6, 2026
Updated: Oct 19, 2026
Reserved: Sep 25, 2026

Description

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

tcp: exclude old ACKs from tcp fast path

Exclude old ACKs before SND.UNA from the tcp fast path as well as ACKs after SND.NXT.

Such ACKs will fall through to the slow path, where tcp_ack() performs the appropriate validation and challenge ACK handling according to RFC5961 and Commit 3d501dd326fb1c7 ("tcp: do not accept ACK of bytes we never sent").

This prevents old ACKs from being accepted or modifying connection state as part of the fast path before appropriate ACK validation is applied. In particular, this prevents payload carried by a segment with an excessively old ACK from advancing RCV.NXT before the ACK is rejected.

Scores

The record has no CVSS score.

Weaknesses

The record names no weakness.

Affected Products

Product	Versions
LinuxLinux	31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 07cacab90290f795bad2e566790f4ba8e84cdf5fAffected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 6eb9b697f50b73b9684e466c1e97f4ca8e947a59Affected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before b86e1e5a4bbcbbccde8b7a3d3486604b581f6628Affected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 1c8448db5cf35a13d82b0c9004ffdb49358883e7Affected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 8309dc2cc360056aa9cd2acfbfc25930798c3b66Affected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before ff037920c688ae6ca1153fec01e90e6782712455Affected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6edAffected 31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before f81e6c3fb06327bc49cdd6e559845293ba06a704Affected
LinuxLinux	4.14Affected before 4.14Not affected 5.10.271 through 5.10.Not affected 5.15.222 through 5.15.Not affected 6.1.189 through 6.1.Not affected 6.6.158 through 6.6.Not affected 6.12.112 through 6.12.Not affected 6.18.54 through 6.18.Not affected 7.2.8 through 7.2.*Not affected 7.3 and laterNot affected

Product

Versions

LinuxLinux

31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 07cacab90290f795bad2e566790f4ba8e84cdf5fAffected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 6eb9b697f50b73b9684e466c1e97f4ca8e947a59Affected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before b86e1e5a4bbcbbccde8b7a3d3486604b581f6628Affected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 1c8448db5cf35a13d82b0c9004ffdb49358883e7Affected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 8309dc2cc360056aa9cd2acfbfc25930798c3b66Affected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before ff037920c688ae6ca1153fec01e90e6782712455Affected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before 8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6edAffected
31770e34e43d6c8dee129bfee77e56c34e61f0e5 to before f81e6c3fb06327bc49cdd6e559845293ba06a704Affected

LinuxLinux

4.14Affected
before 4.14Not affected
5.10.271 through 5.10.*Not affected
5.15.222 through 5.15.*Not affected
6.1.189 through 6.1.*Not affected
6.6.158 through 6.6.*Not affected
6.12.112 through 6.12.*Not affected
6.18.54 through 6.18.*Not affected
7.2.8 through 7.2.*Not affected
7.3 and laterNot affected

References

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