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CVE-2026-53239
xfrm: policy: fix use-after-free on inexact bin in xfrm_policy_bysel_ctx()
Published 2026-06-25 (4 months ago) by the Linux kernel CNA. Subsystem net/xfrm. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-53239 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | fixedDLA-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.13-1 | Update the kernel and reboot. Fixed in 7.0.13-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Fix the race by pruning the bin while still holding xfrm_policy_lock, before dropping it. Use __xfrm_policy_inexact_prune_bin() directly since the lock is already held. The wrapper xfrm_policy_inexact_prune_bin() becomes unused and is removed. Race: CPU0 (XFRM_MSG_DELPOLICY) CPU1 (XFRM_MSG_NEWSPDINFO) ========================== ========================== xfrm_policy_bysel_ctx(): spin_lock_bh(xfrm_policy_lock) bin = xfrm_policy_inexact_lookup() __xfrm_policy_unlink(pol) spin_unlock_bh(xfrm_policy_lock) xfrm_policy_kill(ret) // wide window, lock not held xfrm_hash_rebuild(): spin_lock_bh(xfrm_policy_lock) __xfrm_policy_inexact_flush(): kfree_rcu(bin) // bin freed spin_unlock_bh(xfrm_policy_lock) xfrm_policy_inexact_prune_bin(bin) // UAF: bin is freed
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/xfrm/xfrm_policy.c
- What this is
- NETWORKING [IPSEC]MAINTAINERS section matched on net/xfrm/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_XFRM /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_XFRM
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-06-25 (4 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.13%, higher than 2.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/xfrm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.0 | 5.10.259 | 8fc536e9f685 |
| 5.0 | 5.15.210 | c4c1ea36d83b |
| 5.0 | 6.1.176 | 25c8c7fb3b0b |
| 5.0 | 6.6.143 | 42827d03f800 |
| 5.0 | 6.12.94 | 88697cf98022 |
| 5.0 | 6.18.36 | b5316e2b8614 |
| 5.0 | 7.0.13 | ec82ea4eb220 |
| 5.0 | 7.1 | 7f2d76c9c032 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | tracker |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The vulnerable path is reached through NETLINK_XFRM messages such as XFRM_MSG_DELPOLICY and XFRM_MSG_NEWSPDINFO, which require local netlink access rather than remote packet delivery.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by creating/deleting an inexact XFRM policy while concurrently triggering SPD hash rebuilds, with no required external victim state.
- PR:LPrivileges required, low
- XFRM netlink operations require CAP_NET_ADMIN, but the check is namespace-scoped via netlink_net_capable() and is reachable with CAP_NET_ADMIN in a user-created network namespace on systems allowing user namespaces.
- UI:NUser interaction, none
- No victim action is required; the attacker can issue the needed netlink messages directly.
- S:UScope, unchanged
- The vulnerability corrupts kernel networking/XFRM state within the same kernel security authority and does not cross a hypervisor, IOMMU, or separate trust boundary.
- C:HConfidentiality impact, high
- This is a use-after-free of an XFRM inexact policy bin, and the stale freed object can be dereferenced after attacker-controlled heap reuse, making high confidentiality impact defensible.
- I:HIntegrity impact, high
- The stale bin is not only read but also passed into pruning logic that writes list/rhashtable/seqcount state, so exploitation can plausibly yield memory corruption and control-flow or data integrity compromise.
- A:HAvailability impact, high
- The UAF can trigger kernel memory corruption, KASAN splats, oopses, or panics, giving high availability impact.