# CVE-2026-90088: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

> A remote attacker can cause a denial of service in the Linux kernel by sending a Bluetooth RFCOMM frame with a zero MTU, triggering an infinite loop and memory exhaustion.

- **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-102227, BELL-CVE-2026-90088, DEBIAN-CVE-2026-90088, GHSA-j6jv-mcf5-3925, UBUNTU-CVE-2026-90088

## What is CVE-2026-90088?

CVE-2026-90088 is a denial of service 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:

Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

rfcomm_apply_pn() accepts the MTU value from a remote PN (Parameter
Negotiation) frame without checking for zero. When the remote peer
sends an MTU of zero, d->mtu is set to 0. This causes the sendmsg
path to enter an infinite loop when fragmenting data, as each fragment
has size == min_t(size_t, len, 0) == 0, so the remaining length never
decreases. The infinite allocation of zero-length skbs exhausts all
system memory.

Fix by clamping d->mtu to RFCOMM_DEFAULT_MTU when the negotiated
value is zero, consistent with the initial value assigned in
rfcomm_dlc_alloc().

## Which versions are affected by CVE-2026-90088?


## How do I fix CVE-2026-90088?

Apply the vendor's patch.

## Is CVE-2026-90088 being exploited?

There is no known exploitation of CVE-2026-90088 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90088 and fix it if it is affected.

What it is: CVE-2026-90088 is a denial of service 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-2026-90088 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-2026-90088/ (Markdown: https://insights.sbomify.com/CVE-2026-90088/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90088
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90088
- OSV: https://osv.dev/vulnerability/CVE-2026-90088

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90088/
Summaries are generated and may contain mistakes; the official description above is the record.