CVE-2026-23247: tcp: secure_seq: add back ports to TS offset

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-03-18 · updated 2026-10-30

Description

In the Linux kernel, the following vulnerability has been resolved: tcp: secure_seq: add back ports to TS offset This reverts 28ee1b746f49 ("secure_seq: downgrade to per-host timestamp offsets") tcp_tw_recycle went away in 2017. Zhouyan Deng reported off-path TCP source port leakage via SYN cookie side-channel that can be fixed in multiple ways. One of them is to bring back TCP ports in TS offset randomization. As a bonus, we perform a single siphash() computation to provide both an ISN and a TS offset.

Affected products

Linux kernel: from 4.11 (excl.) before 6.18.17; from 6.19 before 6.19.7; 4.11-rc6, 4.11-rc7, 4.11-rc8, 7.0-rc1, 7.0-rc2; 4.11; 4.10.14 (and their updates) — fixed in 6.18.17, 6.19.7
Linux: from 4.10.14 before 4.11 — fixed in 4.11

How to fix

Upgrade to a fixed version: Linux kernel 6.18.17, 6.19.7; Linux 4.11. Check the vendor advisory for mitigations.

References

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