netfilter: cttimeout: prevent UAF during module unload
CVE-2026-97609 · published 25 Sept 2026
How serious is it
- Severity: high, CVSS score 7 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-97609?
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Who is affected
- Linux Linux: ebfbe67568a734a449203097b02c4ab884257535 to < f664e06699829a31e95675a6864655a6c5f9904f, ebfbe67568a734a449203097b02c4ab884257535 to < 73f353bec62509c776184e49a031c6145cec0d05, ebfbe67568a734a449203097b02c4ab884257535 to < a7fdd86c386b7f7cc72a126389c2cdb55d035221, ebfbe67568a734a449203097b02c4ab884257535 to < 1f69c570a73f2dedf75ea5166d47622d5fa958c1
- Linux Linux: 5.13
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
netfilter: cttimeout: prevent UAF during module unload
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.
Check your whole app
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References
- git.kernel.org/stable/c/f664e06699829a31e95675a6864655a6c5f9904f
- git.kernel.org/stable/c/73f353bec62509c776184e49a031c6145cec0d05
- git.kernel.org/stable/c/a7fdd86c386b7f7cc72a126389c2cdb55d035221
- git.kernel.org/stable/c/1f69c570a73f2dedf75ea5166d47622d5fa958c1
- git.kernel.org/stable/c/fec9b1de0d02de8dafa3cc344bcb91cf28660643
Merged from CVE List. Last updated 26 Oct 2026. All vulnerabilities · RSS · JSON