CVE-2026-72493: Linux Vulnerability (CVSS 9.9)

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).

Metrics

CVSS 3.1

9.9/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

EPSS Probability

0.16%

5.9th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= e9e4dd3267d0c5234c5c0f47440456b10875dec9, < 2fface6e0bbd6314d1d9d071abf2c4d67548511c; >= e9e4dd3267d0c5234c5c0f47440456b10875dec9, < 46762cefe7f4e5bffc1eb467810a7bbb02e461d7; 78b6803a1961369d0b8350ff1f99b7375bbd7a8f; b5d73d9cdd6be22795499890ea928a6f57ef829c; f6533fed1bfa842e391ee50f9a9c5e963c71e579; 2095ab2456da766174cda8bc105d7a7b1bc70e16; f1fdb184aefa8447560e3ea0e605171592ffee41; f75c8a3015422128ca150e81c730bc2a471b5f4a; >= 3.2.71, < 3.3; >= 3.4.111, < 3.5; >= 3.12.48, < 3.13; >= 3.14.54, < 3.15; >= 3.18.22, < 3.19; >= 4.1.9, < 4.2
Linux	Linux	4.2

References

Timeline

Published: Aug 15, 2026
Last Modified: Aug 17, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-72493?

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).

How severe is CVE-2026-72493?

CVE-2026-72493 has a CVSS score of 9.9/10 (CRITICAL severity). The EPSS model estimates a 0.16% probability of exploitation in the next 30 days.

How do I fix CVE-2026-72493?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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