---
id: CVE-2026-64581
title: |-
  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
summary: |-
  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, NUL…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
published: '2026-08-05'
updated: '2026-08-08'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64581'
references:
  - url: 'https://git.kernel.org/stable/c/96b678d08268b5f5c6fc99d4289d9b7e334fc683'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c283e9ada7fcb7dd4b10592623086b2e6d2f9925'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
epss: 0.00171
epssPercentile: 0.05739
ingestedAt: '2026-08-08T21:30:13.001Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.