# CVE-2026-89902: LoongArch: Avoid preempt count underflow without probe

> A local attacker can trigger a preempt count underflow via a userspace breakpoint, bypassing cgroup socket policies and potentially escalating privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 16 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-101619, BELL-CVE-2026-89902, DEBIAN-CVE-2026-89902, GHSA-w2c5-6c3v-2hf7, UBUNTU-CVE-2026-89902

## What is CVE-2026-89902?

CVE-2026-89902 is a high-severity vulnerability in Linux, published on 16 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:

LoongArch: Avoid preempt count underflow without probe

LoongArch uses break 11 for the breakpoint placed after an instruction
that Kprobes executes out of line. Since userspace can issue the same
break instruction, do_bp() can reach kprobe_singlestep_handler() when
there is no current probe.

The handler actually returns false in this case, but it first calls
preempt_enable_no_resched(). The corresponding preempt_disable() is done
by kprobe_breakpoint_handler() on a real Kprobe hit, so it has not run
here. As a result, an ordinary userspace breakpoint (code 11) underflows
the current task's preempt count.

This also makes in_interrupt() return true until the task schedules. One
visible consequence is the socket cgroup attribution: cgroup_sk_alloc()
treats the allocation as interrupt context and assigns the socket to the
root cgroup. A socket opened from the SIGTRAP handler can then avoid a
BPF_CGROUP_INET_SOCK_CREATE policy attached to the task's own cgroup.

Return as soon as kprobe_running() reports no active probe.

The same check has appeared in [PATCH v10 2/4] of the original LoongArch
Kprobes series, but was dropped before the feature reached mainline.

## Which versions are affected by CVE-2026-89902?


## How do I fix CVE-2026-89902?

Apply the vendor's patch.

## Is CVE-2026-89902 being exploited?

There is no known exploitation of CVE-2026-89902 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89902 and fix it if it is affected.

What it is: CVE-2026-89902 is a high-severity vulnerability in Linux, published on 16 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-2026-89902 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-2026-89902/ (Markdown: https://insights.sbomify.com/CVE-2026-89902/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89902
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89902
- OSV: https://osv.dev/vulnerability/CVE-2026-89902

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89902/
Summaries are generated and may contain mistakes; the official description above is the record.