# CVE-2025-21922: ppp: Fix KMSAN uninit-value warning with bpf

> A local attacker can read uninitialized kernel memory via crafted BPF programs in the PPP driver, potentially exposing sensitive data.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 1 Apr 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-59934, AZL-59973, BELL-CVE-2025-21922, DEBIAN-CVE-2025-21922, GHSA-6g9c-7jcv-4g45, ROOT-OS-UBUNTU-2404-CVE-2025-21922, UBUNTU-CVE-2025-21922

## What is CVE-2025-21922?

CVE-2025-21922 is a medium-severity vulnerability in Linux kernel, published on 1 Apr 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:

ppp: Fix KMSAN uninit-value warning with bpf

Syzbot caught an "KMSAN: uninit-value" warning [1], which is caused by the
ppp driver not initializing a 2-byte header when using socket filter.

The following code can generate a PPP filter BPF program:
'''
struct bpf_program fp;
pcap_t *handle;
handle = pcap_open_dead(DLT_PPP_PPPD, 65535);
pcap_compile(handle, &fp, "ip and outbound", 0, 0);
bpf_dump(&fp, 1);
'''
Its output is:
'''
(000) ldh [2]
(001) jeq #0x21 jt 2 jf 5
(002) ldb [0]
(003) jeq #0x1 jt 4 jf 5
(004) ret #65535
(005) ret #0
'''
Wen can find similar code at the following link:
https://github.com/ppp-project/ppp/blob/master/pppd/options.c#L1680
The maintainer of this code repository is also the original maintainer
of the ppp driver.

As you can see the BPF program skips 2 bytes of data and then reads the
'Protocol' field to determine if it's an IP packet. Then it read the first
byte of the first 2 bytes to determine the direction.

The issue is that only the first byte indicating direction is initialized
in current ppp driver code while the second byte is not initialized.

For normal BPF programs generated by libpcap, uninitialized data won't be
used, so it's not a problem. However, for carefully crafted BPF programs,
such as those generated by syzkaller [2], which start reading from offset
0, the uninitialized data will be used and caught by KMSAN.

[1] https://syzkaller.appspot.com/bug?extid=853242d9c9917165d791
[2] https://syzkaller.appspot.com/text?tag=ReproC&x=11994913980000

Weakness: CWE-908 (Use of Uninitialized Resource)

## Which versions are affected by CVE-2025-21922?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21922?

Apply the vendor's patch.

## Is CVE-2025-21922 being exploited?

There is no known exploitation of CVE-2025-21922 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-2025-21922 and fix it if it is affected.

What it is: CVE-2025-21922 is a medium-severity vulnerability in Linux kernel, published on 1 Apr 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-2025-21922 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-2025-21922/ (Markdown: https://insights.sbomify.com/CVE-2025-21922/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21922
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21922
- OSV: https://osv.dev/vulnerability/CVE-2025-21922

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21922/
Summaries are generated and may contain mistakes; the official description above is the record.