Linux Kernel xfrm State Delete slabUAF fix
CVE-2026-46116 Published on May 28, 2026
xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
In the Linux kernel, the following vulnerability has been resolved:
xfrm: defensively unhash xfrm_state lists in __xfrm_state_delete
KASAN reproduces a slab-use-after-free in __xfrm_state_delete()'s
hlist_del_rcu calls under syzkaller load on linux-6.12.y stable
(reproduced on 6.12.47, also reachable via the same code path on
torvalds/master and on the ipsec tree). Nine unique signatures cluster
in the xfrm_state lifecycle, the load-bearing one being:
BUG: KASAN: slab-use-after-free in __hlist_del include/linux/list.h:990 [inline]
BUG: KASAN: slab-use-after-free in hlist_del_rcu include/linux/rculist.h:516 [inline]
BUG: KASAN: slab-use-after-free in __xfrm_state_delete net/xfrm/xfrm_state.c
Write of size 8 at addr ffff8881198bcb70 by task kworker/u8:9/435
Workqueue: netns cleanup_net
Call Trace:
__hlist_del / hlist_del_rcu
__xfrm_state_delete
xfrm_state_delete
xfrm_state_flush
xfrm_state_fini
ops_exit_list
cleanup_net
The other observed signatures hit the same slab object from
__xfrm_state_lookup, xfrm_alloc_spi, __xfrm_state_insert and an OOB
write variant of __xfrm_state_delete, all on the byseq/byspi
hash chains.
__xfrm_state_delete() guards its byseq and byspi unhashes with
value-based predicates:
if (x->km.seq)
hlist_del_rcu(&x->byseq);
if (x->id.spi)
hlist_del_rcu(&x->byspi);
while everywhere else in the file (e.g. state_cache, state_cache_input)
the safer hlist_unhashed() check is used. xfrm_alloc_spi() sets
x->id.spi = newspi inside xfrm_state_lock and then immediately inserts
into byspi, but a path that observes x->id.spi != 0 outside of
xfrm_state_lock can still skip-or-hit the byspi unhash inconsistently
with whether x is actually on the list. The same holds for x->km.seq
versus byseq, and the bydst/bysrc unhashes have no predicate at all,
so a second __xfrm_state_delete() on the same object writes through
LIST_POISON pprev.
The defensive change here:
- Use hlist_del_init_rcu() instead of hlist_del_rcu() on bydst,
bysrc, byseq and byspi so a second deletion is a no-op rather
than a write through LIST_POISON pprev. The byseq/byspi nodes
are already initialised in xfrm_state_alloc().
- Test hlist_unhashed() rather than the value predicate for
byseq/byspi, so the unhash decision tracks list state rather than
mutable scalar fields.
Empirical verification: applied this patch on top of v6.12.47, rebuilt,
and re-ran the same syzkaller harness for 1h16m on a previously-crashy
configuration that produced ~100 hits each of slab-use-after-free
Read in xfrm_alloc_spi / Read in __xfrm_state_lookup / Write in
__xfrm_state_delete. After the patch, 7.1M execs across 32 VMs at
~1550 exec/sec produced zero xfrm_state UAF/OOB hits. /proc/slabinfo
confirms the xfrm_state slab is actively allocated and freed during
the run (~143 KiB resident), so the fuzzer is still exercising those
code paths -- they just no longer crash.
Reproduction:
- Linux 6.12.47 x86_64 + KASAN_GENERIC + KASAN_INLINE + KCOV
- syzkaller @ 746545b8b1e4c3a128db8652b340d3df90ce61db
- 32 QEMU/KVM VMs x 2 vCPU on AWS c5.metal bare metal
- 9 unique signatures collected in ~9h, all within xfrm_state
lifecycle
Vulnerability Analysis
CVE-2026-46116 is exploitable with local system access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Type
Release of Invalid Pointer or Reference
The application attempts to return a memory resource to the system, but calls the wrong release function or calls the appropriate release function incorrectly.
Products Associated with CVE-2026-46116
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Affected Versions
Linux:- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below 3943fcad7694a7d0b15aeabe7d3cc2a2eb8e92e8 is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below 2c617848ae6e4f07a3e397f604208c293bbecacc is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below b4a53add2fa8f1b5aa17d4c5686c320785fab182 is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below 26edb0a3c99f9d958c212be68b21f1221614dcf0 is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below 4980162de555cb838f1a189ce7d2cbf5d2e7b050 is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below a2e2d08fb070fab4947447171f1c4e3ca5a188e5 is affected.
- Version 7b4dc3600e4877178ba94c7fbf7e520421378aa6 and below 14acf9652e5690de3c7486c6db5fb8dafd0a32a3 is affected.
- Version 2.6.19 is affected.
- Before 2.6.19 is unaffected.
- Version 5.15.210, <= 5.15.* is unaffected.
- Version 6.1.176, <= 6.1.* is unaffected.
- Version 6.6.140, <= 6.6.* is unaffected.
- Version 6.12.88, <= 6.12.* is unaffected.
- Version 6.18.30, <= 6.18.* is unaffected.
- Version 7.0.7, <= 7.0.* is unaffected.
- Version 7.1, <= * is unaffected.
- Version 0:6.12.0-55.88.1.el10_0 and below * is unaffected.
- Version 0:4.18.0-553.144.1.rt7.485.el8_10 and below * is unaffected.
- Version 0:4.18.0-553.144.1.el8_10 and below * is unaffected.
- Version 0:5.14.0-687.22.1.el9_8 and below * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.