# CVE-2026-90274: coresight: etm4x: fix underflow for usage of (nrseqstate - 1)

> An integer underflow in the Linux kernel's CoreSight ETM4x driver can cause a denial of service when specific hardware configurations are present.

- **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:** 17 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-102915, BELL-CVE-2026-90274, DEBIAN-CVE-2026-90274, GHSA-2fmc-xx62-q6fm, UBUNTU-CVE-2026-90274

## What is CVE-2026-90274?

CVE-2026-90274 is a vulnerability in Linux, published on 17 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:

coresight: etm4x: fix underflow for usage of (nrseqstate - 1)

According to IHI006H Embedded Trace Macrocell Architecture
Specification[0], TRCSEQEVR<n> is implemented only when
TRCIDR5.NUMSEQSTATE is 0b100, in which case n ranges from 0 to 2;
otherwise, TRCIDR5.NUMSEQSTATE is 0b000.

IOW, the number of usage in the initialisation or setting
TRCSEQEVR<n> with drvdata->nrseqstate - 1 in the loop could make
underflow issue when TRCIDR5.NUMSEQSTATE is 0b000.

Therefore, introduce nr_seq_ctrls field and untie it from nrseqstate.
As part of this introduce ETM_MAX_SEQ_TRANSITIONS macro and
apply nr_seq_ctrls and above macro to TRCSEQEVR<n> relevant fields setup.

## Which versions are affected by CVE-2026-90274?


## How do I fix CVE-2026-90274?

Apply the vendor's patch.

## Is CVE-2026-90274 being exploited?

There is no known exploitation of CVE-2026-90274 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90274 and fix it if it is affected.

What it is: CVE-2026-90274 is a vulnerability in Linux, published on 17 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-2026-90274 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-2026-90274/ (Markdown: https://insights.sbomify.com/CVE-2026-90274/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90274
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90274
- OSV: https://osv.dev/vulnerability/CVE-2026-90274

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90274/
Summaries are generated and may contain mistakes; the official description above is the record.