CVE-2026-64581 is a vulnerability in Linux Kernel
Published on August 5, 2026
xfrm: fix sk_dst_cache double-free in xfrm_user_policy()
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_policy (./include/net/sock.h:2239 ./include/net/sock.h:2256 net/xfrm/xfrm_state.c:3053)
do_ip_setsockopt (net/ipv4/ip_sockglue.c:1347)
ip_setsockopt (net/ipv4/ip_sockglue.c:1417)
do_sock_setsockopt (net/socket.c:2368)
__sys_setsockopt (net/socket.c:2393)
__x64_sys_setsockopt (net/socket.c:2396)
do_syscall_64 (arch/x86/entry/syscall_64.c:94)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
Reachable by an unprivileged user via a user+network namespace.
Use the atomic sk_dst_reset() so the cache is cleared and released with a
single xchg(): whichever side wins releases the dst once, the other sees
NULL and does nothing. Behaviour is otherwise unchanged.
Products Associated with CVE-2026-64581
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Affected Versions
Linux:- Version 2b06cdf3e688b98fcc9945873b5d42792bd4eee0 and below 96b678d08268b5f5c6fc99d4289d9b7e334fc683 is affected.
- Version 2b06cdf3e688b98fcc9945873b5d42792bd4eee0 and below c283e9ada7fcb7dd4b10592623086b2e6d2f9925 is affected.
- Version 72f157be2f81910ae759bfe2e5c2256fc4625645 is affected.
- Version 9e9fe58a92a46c6d154d2901735bf230d91b8507 is affected.
- Version adc1ec6cdc20d430aa01b86497220709b9149466 is affected.
- Version b54033eb1cfd77aba471269ddd804ed8d3e35dea is affected.
- Version c9e82cb34c3c2ee895af01bc899c6ed0bc6eb04a is affected.
- Version 5eef9b51114fcc65651d671add52f267f91b9451 is affected.
- Version 3.16.52 and below 3.17 is affected.
- Version 4.4.163 and below 4.5 is affected.
- Version 3.18.101 and below 3.19 is affected.
- Version 4.1.52 and below 4.2 is affected.
- Version 4.4.123 and below 4.5 is affected.
- Version 4.9.89 and below 4.10 is affected.
- Version 4.14 is affected.
- Before 4.14 is unaffected.
- Version 7.1.6, <= 7.1.* is unaffected.
- Version 7.2-rc4, <= * is unaffected.