CVE-2025-40083
Published Oct 29, 2025
Modified Apr 15, 2026
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.
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References
Other References
https://git.kernel.org/stable/c/1bed56f089f09b465420bf23bb32985c305cfc28
https://git.kernel.org/stable/c/3c2a8994807623c7655ece205667ae2cf74940aa
https://git.kernel.org/stable/c/6ff8e74c8f8a68ec07ef837b95425dfe900d060f
https://git.kernel.org/stable/c/6ffa9d66187188e3068b5a3895e6ae1ee34f9199
https://git.kernel.org/stable/c/71d84658a61322e5630c85c5388fc25e4a2d08b2
https://git.kernel.org/stable/c/99fc137f178797204d36ac860dd8b31e35baa2df
https://git.kernel.org/stable/c/dd831ac8221e691e9e918585b1003c7071df0379
Frequently Asked Questions
What is CVE-2025-40083? +
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.
How do I check if I'm vulnerable to CVE-2025-40083? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.