CVE-2025-40083 net/sched: sch_qfq: Fix null-deref in agg_dequeue
A null pointer dereference in the Linux kernel's QFQ scheduler can cause a system crash, requiring local access and specific network scheduling configuration.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40083?
CVE-2025-40083 is a vulnerability in Linux, published on 29 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official 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.
Which versions are affected by CVE-2025-40083?
How do I fix CVE-2025-40083?
Apply the vendor's patch.
Is CVE-2025-40083 being exploited?
There is no known exploitation of CVE-2025-40083 in the wild and no public exploit code.
Sources
Also known as AZL-69027, BELL-CVE-2025-40083, DEBIAN-CVE-2025-40083, GHSA-wf68-85vc-c49w, ROOT-OS-DEBIAN-11-CVE-2025-40083, ROOT-OS-DEBIAN-12-CVE-2025-40083 and 4 more.