CVE-2026-72493
CriticalCVSS 9.9Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel, in enqueue_to_backlog(), there is a TOCTOU race related to the lockless netif_running() check. The check is moved inside the backlog lock, serializing it with the flush operation and preventing the use-after-free reported by syzbot.
Risk Assessment
The race can lead to use-after-free during network device unregistration, potentially causing system crashes or security breaches.
Recommendation
Apply the Linux kernel update containing this fix to eliminate the race and prevent use-after-free in the networking stack.
Original NVD description (English source)
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 the flush work (which also grabs the lock). We then either queue the packet before the flush runs (so it gets flushed), or check netif_running() after the flush/close completes (so it gets dropped).