CVE-2026-31422

MediumCVSS 5.5

Published: 13/04/2026(UTC)Updated: 14/07/2026(UTC)Translated: 16/07/2026(UTC)NVD NIST

Exploitation Probability (EPSS)

Low risk

0.12%

2th percentile - higher than 2% of all known CVEs

Summary

A vulnerability was found in the Linux kernel's flow classifier (cls_flow) for shared QoS blocks. The flow_change() function calls tcf_block_q() and dereferences q->handle, which is NULL for shared blocks, causing a NULL pointer dereference and system crash.

Risk Assessment

An attacker can deliberately create a flow filter without a fully qualified base class on a shared QoS block, triggering a kernel panic (NULL pointer dereference) and disrupting system operation.

Recommendation

Immediately update the Linux kernel to a version containing the fix that adds a tcf_block_shared() check before accessing block->q and returns -EINVAL for shared blocks.

Original NVD description (English source)

In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_flow: fix NULL pointer dereference on shared blocks flow_change() calls tcf_block_q() and dereferences q->handle to derive a default baseclass. Shared blocks leave block->q NULL, causing a NULL deref when a flow filter without a fully qualified baseclass is created on a shared block. Check tcf_block_shared() before accessing block->q and return -EINVAL for shared blocks. This avoids the null-deref shown below: ======================================================================= KASAN: null-ptr-deref in range [0x0000000000000038-0x000000000000003f] RIP: 0010:flow_change (net/sched/cls_flow.c:508) Call Trace: tc_new_tfilter (net/sched/cls_api.c:2432) rtnetlink_rcv_msg (net/core/rtnetlink.c:6980) [...] =======================================================================