CVE-2026-72493 net: serialize netif_running() check in enqueue_to_backlog()
A race condition in the Linux kernel networking stack allows a use-after-free, potentially leading to code execution or denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72493?
CVE-2026-72493 is a critical use after free vulnerability in Linux, published on 15 Aug 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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 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).
Which versions are affected by CVE-2026-72493?
How do I fix CVE-2026-72493?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-72493 being exploited?
There is no known exploitation of CVE-2026-72493 in the wild and no public exploit code.
Sources
Also known as AZL-96054, BELL-CVE-2026-72493, DEBIAN-CVE-2026-72493, GHSA-hhj5-7x2f-mw3r, UBUNTU-CVE-2026-72493.