Use-after-free in Linux kernel - CVE-2026-74656

Vulnerability details

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to a use-after-free in fib_nhc_update_mtu() when walking the nexthop exception table during MTU updates. A local user can trigger concurrent updates to access a freed fib_nh_exception object and cause a denial of service.

The issue involves insufficient synchronization with PMTU exception updates, and KASAN reported a read-after-free during the vulnerable code path.

Affected software

How to mitigate CVE-2026-74656

External References

• https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a
• https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4
• https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982
• https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761
• https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e
• https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a
• https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16
• https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681

Related Security Bulletins

• Use-after-free in Linux kernel ipv4
• Debian update for linux