CVE-2026-72493

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

net: serialize netif_running() check in enqueue_to_backlog()

Syzbot reported a KASAN slab-use-after-free in fib_rules_lookup().

The root cause is a race condition where packets can escape the backlog

flushing during device unregistration (e.g., during netns exit).

Commit e9e4dd3267d0 ("net: do not process device backlog during unregistration")

introduced a lockless netif_running() check in enqueue_to_backlog() to

prevent queuing packets to an unregistering device.

However, this creates a TOCTOU race window.

A lockless transmitter (like veth_xmit) can pass

the check before dev_close() clears IFF_UP. If the transmitter is then

delayed, flush_all_backlogs() can run and finish before the transmitter

grabs the backlog lock and queues the packet. The packet then escapes

the flush and triggers UAF later when processed.

Fix this by moving the netif_running() check inside the backlog lock.

This serializes the check with

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References