# CVE-2025-21954: netmem: prevent TX of unreadable skbs

> A Linux kernel flaw allows denial of service when redirecting unreadable network memory packets to the transmit path, requiring specific traffic control configurations.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Apr 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21954, DEBIAN-CVE-2025-21954, GHSA-5mxp-4f79-c8g9, UBUNTU-CVE-2025-21954

## What is CVE-2025-21954?

CVE-2025-21954 is a critical denial of service vulnerability in Linux kernel, published on 1 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

netmem: prevent TX of unreadable skbs

Currently on stable trees we have support for netmem/devmem RX but not
TX. It is not safe to forward/redirect an RX unreadable netmem packet
into the device's TX path, as the device may call dma-mapping APIs on
dma addrs that should not be passed to it.

Fix this by preventing the xmit of unreadable skbs.

Tested by configuring tc redirect:

sudo tc qdisc add dev eth1 ingress
sudo tc filter add dev eth1 ingress protocol ip prio 1 flower ip_proto \
	tcp src_ip 192.168.1.12 action mirred egress redirect dev eth1

Before, I see unreadable skbs in the driver's TX path passed to dma
mapping APIs.

After, I don't see unreadable skbs in the driver's TX path passed to dma
mapping APIs.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2025-21954?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21954?

Apply the vendor's patch.

## Is CVE-2025-21954 being exploited?

There is no known exploitation of CVE-2025-21954 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-2025-21954 and fix it if it is affected.

What it is: CVE-2025-21954 is a critical denial of service vulnerability in Linux kernel, published on 1 Apr 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-21954 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-2025-21954/ (Markdown: https://insights.sbomify.com/CVE-2025-21954/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21954
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21954
- OSV: https://osv.dev/vulnerability/CVE-2025-21954

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21954/
Summaries are generated and may contain mistakes; the official description above is the record.