# CVE-2026-53250: xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata()

> A race condition in the Linux kernel XSK module allows malicious userspace to bypass bounds checks, potentially leading to out-of-bounds memory access and code execution.

- **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:** 25 Jun 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-53250, DEBIAN-CVE-2026-53250, GHSA-cx83-hxfr-m85v, ROOT-OS-DEBIAN-13-CVE-2026-53250, ROOT-OS-UBUNTU-2404-CVE-2026-53250, UBUNTU-CVE-2026-53250

## What is CVE-2026-53250?

CVE-2026-53250 is a high-severity vulnerability in Linux kernel, published on 25 Jun 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:

xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata()

The TX metadata area resides in the UMEM buffer which is memory-mapped
and concurrently writable by userspace. In xsk_skb_metadata(),
csum_start and csum_offset are read from shared memory for bounds
validation, then read again for skb assignment. A malicious userspace
application can race to overwrite these values between the two reads,
bypassing the bounds check and causing out-of-bounds memory access
during checksum computation in the transmit path.

Fix this by reading csum_start and csum_offset into local variables
once, then using the local copies for both validation and assignment.

Note that other metadata fields (flags, launch_time) and the cached
csum fields may be mutually inconsistent due to concurrent userspace
writes, but this is benign: the only security-critical invariant is
that each field's validated value is the same one used, which local
caching guarantees.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-53250?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-53250?

Apply the vendor's patch.

## Is CVE-2026-53250 being exploited?

There is no known exploitation of CVE-2026-53250 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-2026-53250 and fix it if it is affected.

What it is: CVE-2026-53250 is a high-severity vulnerability in Linux kernel, published on 25 Jun 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-2026-53250 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-2026-53250/ (Markdown: https://insights.sbomify.com/CVE-2026-53250/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-53250
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-53250
- OSV: https://osv.dev/vulnerability/CVE-2026-53250

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-53250/
Summaries are generated and may contain mistakes; the official description above is the record.