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CVE-2026-98255

Linux: tcp: exclude old ACKs from tcp fast path

Linux LinuxOperating systems
Open in ThreatlineRecord JSON
CVSS
NoneNot scored
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.18%Chance of exploitation activity in the next 30 days, higher than 7% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in07cacab90290f795bad2e566790f4ba8e84cdf5fAlso 6eb9b697f50b73b9684e466c1e97f4ca8e947a59, 1c8448db5cf35a13d82b0c9004ffdb49358883e7 and 2 moreCVE List
Published6 Oct 2026Updated 19 Oct 2026CVE List

What fixes it

  • 07cacab90290f795bad2e566790f4ba8e84cdf5fLinuxCVE List
  • 6eb9b697f50b73b9684e466c1e97f4ca8e947a59LinuxCVE List
  • 1c8448db5cf35a13d82b0c9004ffdb49358883e7LinuxCVE List
  • 8309dc2cc360056aa9cd2acfbfc25930798c3b66LinuxCVE List
  • 8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6edLinuxCVE List

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

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.

Text from CVE List

Affected versions 18

  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before 07cacab90290f795bad2e566790f4ba8e84cdf5fCVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before 6eb9b697f50b73b9684e466c1e97f4ca8e947a59CVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before b86e1e5a4bbcbbccde8b7a3d3486604b581f6628CVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before 1c8448db5cf35a13d82b0c9004ffdb49358883e7CVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before 8309dc2cc360056aa9cd2acfbfc25930798c3b66CVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before ff037920c688ae6ca1153fec01e90e6782712455CVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before 8205ac5ddb42a1843fa8d6a8c295b5c7f4f8c6edCVE List
  • Linuxaffected: 31770e34e43d6c8dee129bfee77e56c34e61f0e5 before f81e6c3fb06327bc49cdd6e559845293ba06a704CVE List
  • Linuxaffected: 4.14CVE List
  • Linuxunaffected: all versions before 4.14CVE List
  • Linuxunaffected: 5.10.271 through 5.10.*CVE List
  • Linuxunaffected: 5.15.222 through 5.15.*CVE List
  • Linuxunaffected: 6.1.189 through 6.1.*CVE List
  • Linuxunaffected: 6.6.158 through 6.6.*CVE List
  • Linuxunaffected: 6.12.112 through 6.12.*CVE List
  • Linuxunaffected: 6.18.54 through 6.18.*CVE List
  • Linuxunaffected: 7.2.8 through 7.2.*CVE List
  • Linuxunaffected: 7.3CVE List

References 8