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CVE-2026-74748
netfilter: ipset: fix refcount race between list:set GC and swap
Published 2026-08-26 (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-2026-74748 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-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.105-1 | Update the kernel and reboot. Fixed in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
__ip_set_put_byindex() resolved the index to a set pointer under RCU, then took ip_set_ref_lock in __ip_set_put() to decrement set->ref. ip_set_swap() holds that same lock while swapping both the ip_set_list slots and the two sets' ref counters, so it can interleave between the dereference and the lock acquisition, leaving the caller to decrement a set whose reference already moved to the other index and hit BUG_ON(set->ref == 0). list_set_gc() reaches this from timer softirq, which the nfnl mutex does not serialize against swap: an expiring list:set member calls list_set_del() -> ip_set_put_byindex() while IPSET_CMD_SWAP runs on the referenced sets. Resolve the index and decrement under ip_set_ref_lock, as ip_set_swap() already does, keeping the refcount tied to the index rather than to a stale set pointer. kernel BUG at net/netfilter/ipset/ip_set_core.c:685! Oops: invalid opcode: 0000 [#1] SMP KASAN NOPTI RIP: 0010:ip_set_put_byindex (net/netfilter/ipset/ip_set_core.c:870) Call Trace: <IRQ> list_set_del (net/netfilter/ipset/ip_set_list_set.c:159) set_cleanup_entries (net/netfilter/ipset/ip_set_list_set.c:181) list_set_gc (net/netfilter/ipset/ip_set_list_set.c:578) call_timer_fn (kernel/time/timer.c:1748) __run_timers (kernel/time/timer.c:1799 kernel/time/timer.c:2374) run_timer_softirq (kernel/time/timer.c:2405) </IRQ> Kernel panic - not syncing: Fatal exception in interrupt
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, sid, bookworm · linux-6.12m
- 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
- 2026-08-26 (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
- 0.14%, higher than 2.9% 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 |
|---|---|---|
| 3.8 | 5.10.266 | 97a01de0c632 |
| 3.8 | 5.15.217 | c21afc7c216a |
| 3.8 | 6.1.184 | b0aab9dd1a34 |
| 3.8 | 6.6.153 | b891e7a6bb06 |
| 3.8 | 6.12.105 | 20cb13a523f0 |
| 3.8 | 6.18.46 | cb20da33839f |
| 3.8 | 7.1.10 | 24ffcb1e1688 |
| 3.8 | 7.2 | 0c8886827165 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | 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
- Exploitation requires issuing IPSET_CMD_SWAP over the NETLINK_NETFILTER socket; nfnetlink is a local userspace-to-kernel control interface, not reachable by remote network packets.
- AC:LAttack complexity, low
- An attacker with CAP_NET_ADMIN controls both sides of the race by creating a timeout-enabled list:set, timing member expiry to drive list_set_gc(), and repeatedly issuing IPSET_CMD_SWAP to interleave with the GC softirq.
- PR:LPrivileges required, low
- IPSET_CMD_SWAP is gated by netlink_net_capable(skb, CAP_NET_ADMIN); CAP_NET_ADMIN is obtainable by unprivileged users inside a user namespace (unshare -Urn), so real init-namespace root is not required.
- UI:NUser interaction, none
- Triggering the refcount race requires only attacker-controlled netlink commands and timer-driven GC; no victim user action such as opening files or mounting filesystems is needed.
- S:UScope, unchanged
- The impact is a kernel BUG/panic and potential memory-safety corruption within the same kernel security domain; it does not cross a VM, container, or IOMMU boundary to affect a separate security authority.
- C:HConfidentiality impact, high
- The refcount race between list_set_gc and ip_set_swap can corrupt set lifetime management; stale pointer decrements can leave sets with incorrect refcounts, enabling use-after-free and arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- Incorrect refcount decrements on stale set pointers can free ip_set objects while still referenced in ip_set_list, providing heap reuse primitives that could be leveraged for arbitrary kernel memory corruption or code execution.
- A:HAvailability impact, high
- The demonstrated failure path hits BUG_ON(set->ref == 0) in timer softirq during list_set_gc, producing a fatal kernel oops and panic that crashes the entire system.