# CVE-2026-31641: rxrpc: Fix RxGK token loading to check bounds

> An integer overflow in the Linux kernel's rxrpc module allows heap buffer overflow via unprivileged key addition, potentially leading to code execution or privilege escalation.

- **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:** 24 Apr 2026
- **Updated:** 20 Aug 2026
- **Also known as:** BELL-CVE-2026-31641, DEBIAN-CVE-2026-31641, GHSA-p4pm-x7ch-5mvc, UBUNTU-CVE-2026-31641

## What is CVE-2026-31641?

CVE-2026-31641 is a high-severity vulnerability in Linux kernel, published on 24 Apr 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:

rxrpc: Fix RxGK token loading to check bounds

rxrpc_preparse_xdr_yfs_rxgk() reads the raw key length and ticket length
from the XDR token as u32 values and passes each through round_up(x, 4)
before using the rounded value for validation and allocation.  When the raw
length is >= 0xfffffffd, round_up() wraps to 0, so the bounds check and
kzalloc both use 0 while the subsequent memcpy still copies the original
~4 GiB value, producing a heap buffer overflow reachable from an
unprivileged add_key() call.

Fix this by:

 (1) Rejecting raw key lengths above AFSTOKEN_GK_KEY_MAX and raw ticket
     lengths above AFSTOKEN_GK_TOKEN_MAX before rounding, consistent with
     the caps that the RxKAD path already enforces via AFSTOKEN_RK_TIX_MAX.

 (2) Sizing the flexible-array allocation from the validated raw key
     length via struct_size_t() instead of the rounded value.

 (3) Caching the raw lengths so that the later field assignments and
     memcpy calls do not re-read from the token, eliminating a class of
     TOCTOU re-parse.

The control path (valid token with lengths within bounds) is unaffected.

Weakness: CWE-190 (Integer Overflow or Wraparound), CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-31641?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31641?

Apply the vendor's patch.

## Is CVE-2026-31641 being exploited?

There is no known exploitation of CVE-2026-31641 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31641 and fix it if it is affected.

What it is: CVE-2026-31641 is a high-severity vulnerability in Linux kernel, published on 24 Apr 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-2026-31641 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31641/ (Markdown: https://insights.sbomify.com/CVE-2026-31641/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31641
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31641
- OSV: https://osv.dev/vulnerability/CVE-2026-31641

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31641/
Summaries are generated and may contain mistakes; the official description above is the record.