# CVE-2026-89759: mm/kmemleak: avoid soft lockup when scanning task stacks

> A local attacker can trigger a soft lockup in the Linux kernel's kmemleak scanner, causing a denial of service on systems with many threads.

- **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:** 11 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-100301, BELL-CVE-2026-89759, DEBIAN-CVE-2026-89759, GHSA-cr6x-j7pj-fq6g, UBUNTU-CVE-2026-89759

## What is CVE-2026-89759?

CVE-2026-89759 is a denial of service vulnerability in Linux, published on 11 Sep 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:

mm/kmemleak: avoid soft lockup when scanning task stacks

Patch series "mm/kmemleak: avoid soft lockup when scanning task", v3.

kmemleak_scan() scans every task stack under one rcu_read_lock() with no
reschedule point, which can trip the soft lockup watchdog on hosts with
very many threads.

That prints the following message, depending on the workload+host
configuration:

      watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
       scan_block
       kmemleak_scan
       kmemleak_scan_thread
       kthread

Patch 1 walks the tasks with find_ge_pid() so the scan reschedules between
tasks

Patches 2-3 let the scan loops stop early once a scan is interrupted.

This patch (of 3):

kmemleak_scan() walks every thread and scans its kernel stack under a
single rcu_read_lock() with no reschedule point.  On a host with very many
threads -- amplified by KASAN/lockdep in debug builds -- this loop can hog
a CPU long enough to trip the soft lockup watchdog:

  watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537]
   scan_block
   kmemleak_scan
   kmemleak_scan_thread
   kthread

A cond_resched() cannot be added directly: the loop runs inside an RCU
read-side critical section.

Walk the tasks one PID at a time with find_ge_pid(), taking the RCU read
lock only to look up and pin each task.  The stack is then scanned with no
lock held, so cond_resched() runs between tasks and the scan stops early
on scan_should_stop().  This follows the next_tgid()/task_seq_get_next()
iteration pattern and keeps each RCU critical section short.

## Which versions are affected by CVE-2026-89759?


## How do I fix CVE-2026-89759?

Apply the vendor's patch.

## Is CVE-2026-89759 being exploited?

There is no known exploitation of CVE-2026-89759 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89759 and fix it if it is affected.

What it is: CVE-2026-89759 is a denial of service vulnerability in Linux, published on 11 Sep 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-2026-89759 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-2026-89759/ (Markdown: https://insights.sbomify.com/CVE-2026-89759/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89759
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89759
- OSV: https://osv.dev/vulnerability/CVE-2026-89759

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89759/
Summaries are generated and may contain mistakes; the official description above is the record.