# CVE-2025-40071: tty: n_gsm: Don't block input queue by waiting MSC

> A local attacker can cause a denial of service in the Linux kernel by blocking the input queue during GSM modem status updates.

- **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:** 28 Oct 2025
- **Updated:** 23 May 2026
- **Also known as:** AZL-68942, BELL-CVE-2025-40071, DEBIAN-CVE-2025-40071, GHSA-xj3g-qjx7-6cfm, ROOT-OS-DEBIAN-12-CVE-2025-40071, ROOT-OS-DEBIAN-13-CVE-2025-40071, ROOT-OS-UBUNTU-2204-CVE-2025-40071, ROOT-OS-UBUNTU-2404-CVE-2025-40071, UBUNTU-CVE-2025-40071

## What is CVE-2025-40071?

CVE-2025-40071 is a denial of service vulnerability in Linux, published on 28 Oct 2025. 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:

tty: n_gsm: Don't block input queue by waiting MSC

Currently gsm_queue() processes incoming frames and when opening
a DLC channel it calls gsm_dlci_open() which calls gsm_modem_update().
If basic mode is used it calls gsm_modem_upd_via_msc() and it
cannot block the input queue by waiting the response to come
into the same input queue.

Instead allow sending Modem Status Command without waiting for remote
end to respond. Define a new function gsm_modem_send_initial_msc()
for this purpose. As MSC is only valid for basic encoding, it does
not do anything for advanced or when convergence layer type 2 is used.

## Which versions are affected by CVE-2025-40071?


## How do I fix CVE-2025-40071?

Apply the vendor's patch.

## Is CVE-2025-40071 being exploited?

There is no known exploitation of CVE-2025-40071 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40071 and fix it if it is affected.

What it is: CVE-2025-40071 is a denial of service vulnerability in Linux, published on 28 Oct 2025. 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-2025-40071 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-2025-40071/ (Markdown: https://insights.sbomify.com/CVE-2025-40071/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40071
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40071
- OSV: https://osv.dev/vulnerability/CVE-2025-40071

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40071/
Summaries are generated and may contain mistakes; the official description above is the record.