CVE-2026-72068 posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()
A local attacker can trigger premature CPU timer expiration on 32-bit Linux kernels via integer overflow, causing potential 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-2026-72068?
CVE-2026-72068 is a 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:
posix-cpu-timers: Use u64 multiplication in update_rlimit_cpu()
update_rlimit_cpu() converts the RLIMIT_CPU value to nanoseconds with
u64 nsecs = rlim_new * NSEC_PER_SEC;
On 32-bit kernels both rlim_new (unsigned long) and NSEC_PER_SEC (1000000000L) are 32-bit, so the multiplication is performed in unsigned long and truncated for rlim_new > 4 seconds before being widened to u64.
The same file already casts to u64 for the matching computation in check_process_timers():
u64 softns = (u64)soft * NSEC_PER_SEC;
As a result, the truncated value is installed into the CPUCLOCK_PROF expiry cache (nextevt), causing the process CPU timer to be programmed to fire prematurely for any RLIMIT_CPU soft limit >= 5 seconds. The actual SIGXCPU/SIGKILL decision in check_process_timers() already casts to u64 and is therefore correct, so limit enforcement is not broken; only the expiry-cache programming is wrong. Apply the same cast here so both paths convert rlim_cur identically.
64-bit kernels are unaffected.
Which versions are affected by CVE-2026-72068?
How do I fix CVE-2026-72068?
Apply the vendor's patch.
Is CVE-2026-72068 being exploited?
There is no known exploitation of CVE-2026-72068 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72068, DEBIAN-CVE-2026-72068, GHSA-8p2j-7pmx-3hp5, UBUNTU-CVE-2026-72068.