CVE-2026-98255

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.

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EPSS — Exploit Prediction

0.0018

Probability of exploitation

0.07%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

References

Other References

https://git.kernel.org/stable/c/07cacab90290f795bad2e566790f4ba8e84cdf5f https://git.kernel.org/stable/c/1c8448db5cf35a13d82b0c9004ffdb49358883e7 https://git.kernel.org/stable/c/6eb9b697f50b73b9684e466c1e97f4ca8e947a59 https://git.kernel.org/stable/c/8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6ed https://git.kernel.org/stable/c/8309dc2cc360056aa9cd2acfbfc25930798c3b66 https://git.kernel.org/stable/c/b86e1e5a4bbcbbccde8b7a3d3486604b581f6628 https://git.kernel.org/stable/c/f81e6c3fb06327bc49cdd6e559845293ba06a704 https://git.kernel.org/stable/c/ff037920c688ae6ca1153fec01e90e6782712455

Frequently Asked Questions

What is CVE-2026-98255? +

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.

How do I check if I'm vulnerable to CVE-2026-98255? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.