# CVE-2026-74749: rseq: Prevent hard lockup on granted time slice extension

> A local attacker can cause a hard lockup in the Linux kernel by triggering a race condition in the rseq time slice extension mechanism.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Aug 2026
- **Updated:** 26 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-74749, UBUNTU-CVE-2026-74749

## What is CVE-2026-74749?

CVE-2026-74749 is a denial of service vulnerability in Linux, published on 26 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:

rseq: Prevent hard lockup on granted time slice extension

__exit_to_user_mode_loop() invokes rseq_grant_timeslice_extension() with
interrupts enabled. If the extension is granted it invokes
hrtimer_rearm_deferred_tif() to ensure that a pending deferred hrtimer
rearm is handled before exiting to user space.

Though this invokes __hrtimer_rearm_deferred() which expects to be invoked
with interrupts disabled as it takes hrtimer_cpu_base::lock with
raw_spin_lock(). That's a livelock waiting to happen and caught by lockdep:

    WARNING: ./include/linux/hrtimer_rearm.h:17 at irqentry_exit, CPU#1: slice_test
    WARNING: inconsistent lock state
    inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage.

Prevent this by disabling interrupts around the invocation of
hrtimer_rearm_deferred_tif() in rseq_grant_timeslice_extension().

[ tglx: Massaged change log ]

## Which versions are affected by CVE-2026-74749?


## How do I fix CVE-2026-74749?

Apply the vendor's patch.

## Is CVE-2026-74749 being exploited?

There is no known exploitation of CVE-2026-74749 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74749 and fix it if it is affected.

What it is: CVE-2026-74749 is a denial of service vulnerability in Linux, published on 26 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-2026-74749 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-2026-74749/ (Markdown: https://insights.sbomify.com/CVE-2026-74749/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74749
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74749
- OSV: https://osv.dev/vulnerability/CVE-2026-74749

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74749/
Summaries are generated and may contain mistakes; the official description above is the record.