CVE-2025-38556 HID: core: Harden s32ton() against conversion to 0 bits
A malicious HID device with a zero-bit report field can cause a kernel crash via shift-out-of-bounds, leading to 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-2025-38556?
CVE-2025-38556 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Aug 2025. 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:
HID: core: Harden s32ton() against conversion to 0 bits
Testing by the syzbot fuzzer showed that the HID core gets a shift-out-of-bounds exception when it tries to convert a 32-bit quantity to a 0-bit quantity. Ideally this should never occur, but there are buggy devices and some might have a report field with size set to zero; we shouldn't reject the report or the device just because of that.
Instead, harden the s32ton() routine so that it returns a reasonable result instead of crashing when it is called with the number of bits set to 0 -- the same as what snto32() does.
Weakness: CWE-125
Which versions are affected by CVE-2025-38556?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-38556?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-38556 being exploited?
There is no known exploitation of CVE-2025-38556 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-66491, AZL-70460, BELL-CVE-2025-38556, DEBIAN-CVE-2025-38556, GHSA-fr7f-qh29-24jq, ROOT-OS-DEBIAN-11-CVE-2025-38556 and 5 more.