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CVE-2026-52920
netfilter: xt_policy: fix strict mode inbound policy matching
Published 2026-06-24 (4 months ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-52920 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 | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
match_policy_in() walks sec_path entries from the last transform to the first one, but strict policy matching needs to consume info->pol[] in the same forward order as the rule layout. Derive the strict-match policy position from the number of transforms already consumed so that multi-element inbound rules are matched consistently.
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/netfilter/xt_policy.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- xt_policy
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NETFILTER_XT_MATCH_POLICY' /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.
lsmod | grep -w xt_policyPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded.
- bookworm, trixie, forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NETFILTER_XT_MATCH_POLICY
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-06-24 (4 months ago)source
- CVSS
- 8.3 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.30%, higher than 21.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.17 | 5.10.258 | eb323f7b82d2 |
| 2.6.17 | 5.15.209 | fc1c518bb1f0 |
| 2.6.17 | 6.1.175 | f98b7f85e04b |
| 2.6.17 | 6.6.141 | 82664d0f1ba2 |
| 2.6.17 | 6.12.91 | b130a6eefa02 |
| 2.6.17 | 6.18.33 | 938867e870fb |
| 2.6.17 | 7.0.10 | 392cc1d8408b |
| 2.6.17 | 7.1 | 4b2b4d7d4e20 |
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:NAttack vector, network
- The vulnerable matcher is executed while processing inbound IPv4/IPv6 packets through x_tables after XFRM/IPsec has populated the packet sec_path. A remote IPsec peer can trigger the affected strict inbound policy rule by sending network packets in a realistic VPN/gateway deployment.
- AC:LAttack complexity, low
- Exploitation requires a strict inbound xt_policy rule with multiple policy elements and a packet with the same number of transforms, but those are normal affected configurations rather than attacker-uncontrolled races. Once present, triggering is repeatable by sending matching packets.
- PR:LPrivileges required, low
- Unauthenticated packets generally fail XFRM state/authentication before reaching this sec_path-based match, so the network scenario requires an authorized IPsec peer or equivalent low privilege. Locally, the rule/XFRM setup is gated by CAP_NET_ADMIN in the network namespace, which is reachable through user namespaces.
- UI:NUser interaction, none
- No victim user action is needed after the vulnerable rule/state configuration exists. Packet delivery or local namespace traffic is sufficient to invoke the matcher.
- S:UScope, unchanged
- The bug is in kernel netfilter/XFRM policy evaluation and impacts the same kernel/network security authority. It does not cross a VM, IOMMU, or separate sandbox security scope.
- C:HConfidentiality impact, high
- The old strict inbound index calculation can make pos negative and read before info->pol[], including x_tables rule metadata or adjacent kernel allocation contents. Although exposed through match behavior rather than a direct copy_to_user, this is an out-of-bounds kernel read larger than a few bytes, so the higher confidentiality impact is warranted.
- I:LIntegrity impact, low
- The bug does not provide a direct write primitive or code execution path, but it can make strict IPsec policy matching produce incorrect firewall decisions. That can bypass or misapply intended packet filtering for affected multi-element inbound rules.
- A:HAvailability impact, high
- The negative-index read can reach outside the intended match data and, for larger strict transform counts or unlucky layout, may fault/oops in kernel packet processing. The condition can be triggered repeatedly with packets once the affected rule path is reachable.