CVE-2026-31741 counter: rz-mtu3-cnt: prevent counter from being toggled multiple times
A race condition in the rz-mtu3-cnt Linux kernel driver allows runtime PM usage count underflow and invalid hardware access, potentially causing system instability or denial of service.
- 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-2026-31741?
CVE-2026-31741 is a medium-severity vulnerability in Linux kernel, published on 1 May 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:
counter: rz-mtu3-cnt: prevent counter from being toggled multiple times
Runtime PM counter is incremented / decremented each time the sysfs enable file is written to.
If user writes 0 to the sysfs enable file multiple times, runtime PM usage count underflows, generating the following message.
rz-mtu3-counter rz-mtu3-counter.0: Runtime PM usage count underflow!
At the same time, hardware registers end up being accessed with clocks off in rz_mtu3_terminate_counter() to disable an already disabled channel.
If user writes 1 to the sysfs enable file multiple times, runtime PM usage count will be incremented each time, requiring the same number of 0 writes to get it back to 0.
If user writes 0 to the sysfs enable file while PWM is in progress, PWM is stopped without counter being the owner of the underlying MTU3 channel.
Check against the cached count_is_enabled value and exit if the user is trying to set the same enable value.
Which versions are affected by CVE-2026-31741?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31741?
Apply the vendor's patch.
Is CVE-2026-31741 being exploited?
There is no known exploitation of CVE-2026-31741 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31741, DEBIAN-CVE-2026-31741, GHSA-gh23-6p4g-c667, ROOT-OS-UBUNTU-2404-CVE-2026-31741, UBUNTU-CVE-2026-31741.