CVE-2026-23247 tcp: secure_seq: add back ports to TS offset
An off-path attacker can leak TCP source ports via a SYN cookie side-channel, potentially aiding further attacks.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23247?
CVE-2026-23247 is a medium-severity vulnerability in Linux kernel, published on 18 Mar 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-23247?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-23247?
Apply the vendor's patch.
Is CVE-2026-23247 being exploited?
There is no known exploitation of CVE-2026-23247 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-80001, BELL-CVE-2026-23247, DEBIAN-CVE-2026-23247, GHSA-4hcm-qg7j-cc3v, ROOT-OS-DEBIAN-11-CVE-2026-23247, ROOT-OS-DEBIAN-12-CVE-2026-23247 and 4 more.