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.
Affected versions
Linux kernel versions
4.14
and later are affected. Fixed in
5.10.271,
5.15.222,
6.1.189,
6.6.158,
6.12.112,
6.18.54,
7.2.8,
7.3-rc4
and their respective stable series.
References
8 totalFrequently asked questions
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What is CVE-2026-98255?
CVE-2026-98255 is a unscored severity Linux kernel vulnerability . It affects Linux kernel versions from 4.14 onward and has been patched in 5.10.271, 5.15.222, 6.1.189 and others. CVE-2026-98255 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.
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Is there a patch available for CVE-2026-98255?
Yes. CVE-2026-98255 has been patched. Fixed versions include 5.10.271, 5.15.222, 6.1.189 and others. If you are running Linux kernel 4.14 or later up to the fix versions, apply the relevant patch for your kernel branch.
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Is CVE-2026-98255 actively exploited?
No. CVE-2026-98255 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.