CVE-2026-31422 net/sched: cls_flow: fix NULL pointer dereference on shared blocks
A NULL pointer dereference in the Linux kernel's cls_flow scheduler allows local attackers to cause a denial of service via crafted network filters.
- 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-2026-31422?
CVE-2026-31422 is a medium-severity vulnerability in Linux kernel, published on 13 Apr 2026. 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: 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) [...] =======================================================================
Weakness: CWE-476
Which versions are affected by CVE-2026-31422?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31422?
Apply the vendor's patch.
Is CVE-2026-31422 being exploited?
There is no known exploitation of CVE-2026-31422 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-82703, BELL-CVE-2026-31422, DEBIAN-CVE-2026-31422, GHSA-6pmm-j8mh-qwgf, ROOT-OS-DEBIAN-11-CVE-2026-31422, ROOT-OS-DEBIAN-12-CVE-2026-31422 and 4 more.