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CVE-2026-97609
netfilter: cttimeout: prevent UAF during module unload
Published 2026-09-25 (24 days 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-2026-97609 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.7-1 | Update the kernel and reboot. Fixed in 7.2.7-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
nf_ct_set_timeout() protects the timeout hook dereference and policy lookup with rcu_read_lock(). cttimeout_exit(), however, unregisters the per-net operations before it clears the hook. This allows the following interleaving: CPU 0 CPU 1 cttimeout_exit() nf_ct_set_timeout() unregister_pernet_subsys() rcu_read_lock() kfree(pernet) h = nf_ct_timeout_hook h->timeout_find_get() nfct_timeout_pernet() The hook still points to ctnl_timeout_find_get() when CPU 1 looks up the already freed per-net timeout list. KASAN reported: BUG: KASAN: slab-use-after-free in ctnl_timeout_find_get Read of size 8 by task poc/90 Call Trace: ctnl_timeout_find_get+0x271/0x2a0 [nfnetlink_cttimeout] nf_ct_set_timeout+0x7b/0x3c0 xt_ct_tg_check+0x724/0xb20 xt_check_target+0x234/0xa90 do_ipt_set_ctl+0x570/0x1270 Allocated by task 89: __kmalloc_noprof+0x16e/0x460 ops_init+0x6d/0x420 register_pernet_operations+0x2f6/0x670 Freed by task 91: kfree+0x131/0x390 ops_undo_list+0x3d4/0x730 unregister_pernet_operations+0x232/0x490 unregister_pernet_subsys+0x1c/0x30 cttimeout_exit+0x52/0x970 [nfnetlink_cttimeout] Clear the hook and wait for existing readers before unregistering the per-net operations. This blocks new policy lookups and ensures readers that observed the hook finish before the per-net storage 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/netfilter/nfnetlink_cttimeout.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nfnetlink_cttimeout
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_CT_NETLINK_TIMEOUT' /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 nfnetlink_cttimeoutPrints 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_NF_CT_NETLINK_TIMEOUT
- 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
- 2026-09-25 (24 days ago)source
- CVSS
- 7.0 high
CVSS:3.1/AV:L/AC:H/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 3.0% 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 |
|---|---|---|
| 5.13 | 6.12.112 | 73f353bec625 |
| 5.13 | 6.18.53 | a7fdd86c386b |
| 5.13 | 7.2.7 | 1f69c570a73f |
| 5.13 | 7.3 | fec9b1de0d02 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | 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 reader that hits freed memory is reached only by a local setsockopt: do_ipt_set_ctl() -> xt_ct_tg_check() -> nf_ct_set_timeout() -> ctnl_timeout_find_get(), installing an iptables CT target with a timeout policy. No packet from a remote peer carries data into this path.
- AC:HAttack complexity, high
- The free happens only when cttimeout_exit() runs, i.e. an admin unloading nfnetlink_cttimeout. The attacker must hit the short window between unregister_pernet_subsys() freeing the per-net list and RCU_INIT_POINTER(nf_ct_timeout_hook, NULL). An unprivileged attacker cannot cause that unload.
- PR:LPrivileges required, low
- The racing side needs only CAP_NET_ADMIN over the netns, which an unprivileged user gets via unshare -Urn and then installs a CT --timeout rule through iptables set_ctl. The unload is the admin's action, not a privilege the attacker must hold.
- UI:NUser interaction, none
- No victim has to open, mount or run anything on the attacker's behalf. The attacker only needs to be running its setsockopt loop while the module unload happens (already counted in AC:H).
- S:UScope, unchanged
- The use-after-free is in kernel heap memory (the nfct_timeout_pernet list head) inside the same kernel security authority. No VM or hardware isolation boundary is crossed.
- C:HConfidentiality impact, high
- ctnl_timeout_find_get() walks nfct_timeout_list inside the freed per-net storage. If that memory is reallocated with attacker data, the walk follows a fake list to a fake ctnl_timeout, and that pointer is returned to nf_ct_set_timeout(), enabling reads of kernel memory.
- I:HIntegrity impact, high
- Following a forged list entry, the code increments a refcount on the attacker-chosen object and stores the returned nf_ct_timeout pointer in the conntrack template's timeout extension. That gives a write primitive and a controlled object pointer that can be used for memory corruption.
- A:HAvailability impact, high
- Dereferencing freed per-net memory in ctnl_timeout_find_get() produces a KASAN slab-use-after-free (shown in the fix commit), and on production kernels can oops or corrupt the heap and crash the system.