Linux Kernel up to 7.1.4 enqueue_to_backlog use after free

Summaryinfo

A vulnerability, which was classified as very critical, was found in Linux Kernel up to 7.1.4. This affects the function enqueue_to_backlog. Executing a manipulation can lead to use after free. This vulnerability is registered as CVE-2026-72493. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as very critical was found in Linux Kernel up to 7.1.4. This vulnerability affects the function enqueue_to_backlog. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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).

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-72493 since 08/09/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 08/15/2026).

Upgrading to version 7.1.5 or 7.2-rc1 eliminates this vulnerability. Applying the patch 2fface6e0bbd6314d1d9d071abf2c4d67548511c/46762cefe7f4e5bffc1eb467810a7bbb02e461d7 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4

License

• open-source

Website

• Vendor: https://www.kernel.org/

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