CVE-2026-64581

Technical Description

In the Linux kernel, the following vulnerability has been resolved:

xfrm: fix sk_dst_cache double-free in xfrm_user_policy()

xfrm_user_policy() clears the socket dst cache with __sk_dst_reset(),

i.e. the non-atomic __sk_dst_set(sk, NULL): it reads sk_dst_cache with

rcu_dereference_protected(), stores NULL and dst_release()s the old dst.

That is only safe if no other thread modifies sk_dst_cache concurrently.

For a connected UDP socket that does not hold: the transmit fast path

(udp_sendmsg -> sk_dst_check -> sk_dst_reset) resets the cache locklessly

with an atomic xchg(). A per-socket policy change racing a send can make

both sides observe the same old dst and each dst_release() it, dropping

the socket's single reference twice and freeing the xfrm_dst bundle while

it is still referenced:

BUG: KASAN: slab-use-after-free in dst_release

Write of size 4 at addr ffff88801897b6c0 by task exploit/155

Call Trace:

...

dst_release (... ./include/linux/rcuref.h:109)

xfrm_user_p

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References