# CVE-2026-80727: x86/mce: Set up the polling timer before CMCI discovery

> A race condition in the Linux kernel x86 MCE subsystem causes a kernel warning and potential instability during CPU initialization.

- **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:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** BELL-CVE-2026-80727, DEBIAN-CVE-2026-80727, GHSA-5fmr-wwgg-gfqm, UBUNTU-CVE-2026-80727

## What is CVE-2026-80727?

CVE-2026-80727 is a vulnerability in Linux, published on 3 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:

x86/mce: Set up the polling timer before CMCI discovery

I hit the following on one of my machines:

  mce: CPU0 BANK15 CMCI inherited storm
  ------------[ cut here ]------------
  ODEBUG: assert_init not available (active state 0) object: (____ptrval____) object type: timer_list hint: 0x0
  WARNING: lib/debugobjects.c:632 at debug_object_assert_init+0x178/0x230, CPU#0: swapper/0/0
  CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 7.2.0-rc5 #3 PREEMPTLAZY
  RIP: 0010:debug_object_assert_init+0x18f/0x230
  Call Trace:
   <TASK>
   __mod_timer
   mce_timer_kick
   cmci_discover
   intel_init_cmci
   mce_intel_feature_init
   mcheck_cpu_init
   identify_cpu
   identify_boot_cpu
   arch_cpu_finalize_init
   start_kernel

A second splat follows right after, from timer_setup() finding that same
timer already queued:

  ODEBUG: init active (active state 0) object: (____ptrval____) object type: timer_list hint: stub_timer+0x0/0x10

This is happening because CMCI storm detection is trying to modify the timer
before latter was properly set up.

Set up the timer first. __mcheck_cpu_setup_timer() only calls timer_setup(),
and depends on neither the generic nor the vendor init.

  [ bp: Massage commit message. ]

## Which versions are affected by CVE-2026-80727?


## How do I fix CVE-2026-80727?

Apply the vendor's patch.

## Is CVE-2026-80727 being exploited?

There is no known exploitation of CVE-2026-80727 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80727 and fix it if it is affected.

What it is: CVE-2026-80727 is a vulnerability in Linux, published on 3 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-2026-80727 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-2026-80727/ (Markdown: https://insights.sbomify.com/CVE-2026-80727/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80727
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80727
- OSV: https://osv.dev/vulnerability/CVE-2026-80727

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80727/
Summaries are generated and may contain mistakes; the official description above is the record.