CVE-2026-72347 netfilter: xt_connmark: reject invalid shift parameters
A local attacker can cause a kernel crash or undefined behavior by installing a netfilter rule with invalid shift parameters in the connmark target.
- 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-2026-72347?
CVE-2026-72347 is a high-severity vulnerability in Linux, published on 15 Aug 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:
netfilter: xt_connmark: reject invalid shift parameters
Revision 2 of the CONNMARK target accepts user-controlled shift parameters and applies them to 32-bit mark values in connmark_tg_shift().
A shift_bits value of 32 or more triggers an undefined-shift bug when the rule is evaluated. Invalid shift_dir values are also accepted and silently fall back to the left-shift path.
Reject invalid revision-2 shift parameters in connmark_tg_check() so malformed rules fail at installation time, before they can reach the packet path.
Which versions are affected by CVE-2026-72347?
How do I fix CVE-2026-72347?
Apply the vendor's patch.
Is CVE-2026-72347 being exploited?
There is no known exploitation of CVE-2026-72347 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72347, DEBIAN-CVE-2026-72347, GHSA-5j52-34gv-x96c, UBUNTU-CVE-2026-72347.