Linux Kernel sched sch_qfq null pointer dereference

Summaryinfo

A vulnerability classified as critical has been found in Linux Kernel. This vulnerability affects the function sch_qfq of the component sched. Performing a manipulation results in null pointer dereference. This vulnerability is cataloged as CVE-2025-40083. There is no exploit available. It is recommended to apply a patch to fix this issue.

Detailsinfo

A vulnerability classified as critical has been found in Linux Kernel (version now known). This affects the function sch_qfq of the component sched. The manipulation with an unknown input leads to a null pointer dereference vulnerability. CWE is classifying the issue as CWE-476. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. This is going to have an impact on availability. The summary by CVE is:

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.

It is possible to read the advisory at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-40083 since 04/16/2025. Technical details of the vulnerability are known, but there is no available exploit.

The vulnerability scanner Nessus provides a plugin with the ID 271974 (Linux Distros Unpatched Vulnerability : CVE-2025-40083), which helps to determine the existence of the flaw in a target environment.

Applying the patch dd831ac8221e691e9e918585b1003c7071df0379 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org.

The vulnerability is also documented in the databases at Tenable (271974), EUVD (EUVD-2025-36665) and CERT Bund (WID-SEC-2025-2441). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Debian Linux
• Amazon Linux 2
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• Open Source Linux Kernel
• Dell NetWorker

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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