Improper input validation in Linux kernel - CVE-2026-98255
Published: October 7, 2026
Vulnerability identifier: #VU153763
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-98255
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to improperly modify TCP connection state.
The vulnerability exists due to improper acknowledgment validation in the TCP receive fast path of tcp_rcv_established() when processing segments with acknowledgment sequence numbers before SND.UNA. A remote attacker can send a TCP segment carrying payload and an excessively old acknowledgment to improperly modify TCP connection state.
The segment's sequence number must match RCV.NXT, and its TCP flags must match the fast-path prediction flags.
Affected software
Linux kernel
Debian Linux
linux (Debian package)
Debian Linux
linux (Debian package)
How to mitigate CVE-2026-98255
Install security update from vendor's repository.
Linux kernel - update to 7.0 rc3
linux (Debian package) - update to 6.12.113-1
linux (Debian package) - update to 6.12.113-1
External 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