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CVE-2026-72435
netfilter: ipset: fix order of kfree_rcu() and rcu_assign_pointer()
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-2026-72435 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 kfree_rcu() was called before rcu_assign_pointer() in handling the comment extension. Fix the order so that rcu_assign_pointer() called first.
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_core.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- ip_set
Check it on the machine
grep -wE 'CONFIG_IP_SET|CONFIG_NETFILTER' /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 ip_setPrints 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_IP_SET, CONFIG_NETFILTER
- 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
- 2026-08-15 (2 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
- 0.17%, higher than 5.8% 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 | 5.10.261 | c9787d7c24ff |
| 4.2 | 5.15.212 | 6e98407cb94e |
| 4.2 | 6.1.178 | 50b70f56f3ba |
| 4.2 | 6.6.145 | d01b4b471f0f |
| 4.2 | 6.12.97 | fcb565966534 |
| 4.2 | 6.18.40 | 8087bb360a93 |
| 4.2 | 7.1.5 | 93a775fd67f3 |
| 4.2 | 7.2 | 3ca9982a8882 |
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 bug is reached only through nfnetlink IPSET commands (ADD/DEL/LIST/SAVE) on NETLINK_GENERIC; nfnetlink_rcv() requires CAP_NET_ADMIN and no remote packet path feeds comment free/replace, so kernel CNA guidance treats netfilter/ipset netlink as Local.
- AC:LAttack complexity, low
- LIST/SAVE dump runs asynchronously without holding the nfnl mutex while mtype_list holds rcu_read_lock and calls ip_set_put_comment; an attacker with CAP_NET_ADMIN can concurrently issue ADD/--exist comment replacement, DEL/flush, or timeout GC to hit the kfree_rcu-before-NULL ordering reliably.
- PR:LPrivileges required, low
- nfnetlink_rcv() gates every ipset command on netlink_net_capable(skb, CAP_NET_ADMIN), which resolves to ns_capable(sock_net()->user_ns, CAP_NET_ADMIN); unprivileged users obtain this inside a user/network namespace via unshare -Urn and fully control per-netns ipset configuration.
- UI:NUser interaction, none
- Exploitation is fully attacker-driven through netlink: create a comment-enabled set, start LIST/SAVE dump, and concurrently add/delete/flush elements or let timeout GC run; no victim click, mount, or other deliberate action is required beyond ordinary local control.
- S:UScope, unchanged
- The RCU use-after-free corrupts kernel heap memory and can yield host privilege escalation or crash, but impact stays within the same kernel security authority and does not cross VM/host, container/host, or IOMMU boundaries.
- C:HConfidentiality impact, high
- Calling kfree_rcu() before rcu_assign_pointer(NULL) lets dump readers under rcu_read_lock still rcu_dereference(comment->c) and nla_put_string() reads freed ip_set_comment_rcu kmalloc memory—a classic UAF read usable for arbitrary kernel disclosure with heap grooming.
- I:HIntegrity impact, high
- Concurrent free and replacement of RCU-managed comment objects lets an attacker reclaim and control freed slab memory, providing standard paths to arbitrary kernel writes, metadata corruption, and control-flow hijack rather than a bounded or crash-only integrity effect.
- A:HAvailability impact, high
- Stale comment pointer dereference during dump or subsequent slab reuse can immediately kernel-oops or panic the host, and the underlying UAF heap corruption can crash or hang the system even when full exploitation is not attempted.