# 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.

- **Severity:** Not scored
- **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:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 17 Aug 2026
- **Also known as:** BELL-CVE-2026-72068, DEBIAN-CVE-2026-72068, GHSA-8p2j-7pmx-3hp5, UBUNTU-CVE-2026-72068

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72068 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-72068 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72068/ (Markdown: https://insights.sbomify.com/CVE-2026-72068/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72068
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72068
- OSV: https://osv.dev/vulnerability/CVE-2026-72068

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72068/
Summaries are generated and may contain mistakes; the official description above is the record.