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CVE-2026-72436
netfilter: ipset: Don't use test_bit() in lockless RCU readers in hash types
Published 2026-08-15 (2 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-2026-72436 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Sashiko pointed out that there are a few lockless RCU readers using test_bit() which is a relaxed atomic operation and provides no memory barrier guarantees. Use test_bit_acquire() instead where the operation may run parallel with add/del/gc, i.e. is not one from the next cases - protected by region lock - in a set destroy phase - in a new/temporary set creation phase
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/ipset/ip_set_hash_gen.h
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
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
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.71%, higher than 52.7% 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 |
|---|---|---|
| 4.2 | 6.1.178 | c107233d2ff4 |
| 4.2 | 6.6.145 | 6329d3a9afe7 |
| 4.2 | 6.12.97 | 7445fe965b7d |
| 4.2 | 6.18.40 | c4d257734e91 |
| 4.2 | 7.1.5 | 3219d74e4536 |
| 4.2 | 7.2 | e4b4984e28c1 |
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 mtype_test() runs on every packet matched by iptables/nftables xt_set rules in PREROUTING/INPUT/FORWARD, so a remote attacker reaches the bug by sending network traffic to internet-facing servers using ipset-based firewall blocklists.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by flooding packets that trigger lockless RCU readers while concurrently driving hash add/del via SET target rules or timeout GC on the same ipset, making the memory-ordering race reliably winnable.
- PR:NPrivileges required, none
- No credentials or local access are required on the target; exploitation needs only unauthenticated network packets to a host running ipset netfilter rules, a standard deployment on firewalls, mail servers, and CDN edge nodes.
- UI:NUser interaction, none
- No victim interaction is needed; the attack is fully automated by sending network traffic and does not require mounting filesystems, opening files, or any other user action.
- S:UScope, unchanged
- The vulnerability corrupts or leaks kernel heap data within the same host security boundary; it does not cross VM, container, or IOMMU isolation boundaries.
- C:HConfidentiality impact, high
- Without acquire semantics, test_bit() can observe a slot as used before element writes are visible or after deletion, causing reads of uninitialized, stale, or freed hbucket element and extension memory—a UAF-class kernel information disclosure.
- I:HIntegrity impact, high
- Stale or torn reads of hash bucket elements during concurrent add/del/gc constitute kernel heap memory safety violations that can corrupt netfilter matching decisions and be further leveraged for control-flow or data manipulation attacks.
- A:HAvailability impact, high
- Reading partially initialized or post-destroy hash element memory during softirq packet processing on loaded firewall datapaths can trigger kernel oopses, panics, or hangs, causing complete loss of availability.