CVE-2026-74660

Summary

In the Linux kernel, the following vulnerability has been resolved:

netfilter: ebt_nflog: pin the NFLOG backend

nf_log_unregister() runs after the per-net teardown so its final RCU grace period also drains readers that obtained the logger from a per-net binding. However, ebt_nflog passes an explicit ULOG log type to nf_log_packet() without holding a reference on the selected logger module, unlike the xt_NFLOG and nft_log frontends.

An ebtables nflog rule can therefore remain callable while nfnetlink_log is unloaded. The resulting interleaving is:

CPU 0 CPU 1 nfnetlink_log_fini() unregister_pernet_subsys() kfree(nfnl_log_pernet(net)) ebt_nflog_tg() nf_log_packet() nfulnl_log_packet() instance_lookup_get_rcu()

The global ULOG logger is still registered at this point, so CPU 1 dereferences the per-net state after CPU 0 has freed it. KASAN reported:

BUG: KASAN: slab-use-after-free in instance_lookup_get_rcu Read of size 8 at addr ff110001052e6210 by task poc/92 Call Trace: instance_lookup_get_rcu+0x1ce/0x1f0 [nfnetlink_log] nfulnl_log_packet+0x248/0x2fb0 [nfnetlink_log] nf_log_packet+0x204/0x300 ebt_nflog_tg+0x351/0x550 ebt_do_table+0xedf/0x22b0 Allocated by task 90: __kmalloc_noprof+0x186/0x470 ops_init+0x6d/0x420 register_pernet_operations+0x2f6/0x670 register_pernet_subsys+0x23/0x40 Freed by task 93: kfree+0x131/0x3c0 ops_undo_list+0x3e3/0x700 unregister_pernet_operations+0x232/0x490 unregister_pernet_subsys+0x1c/0x30 nfnetlink_log_fini+0x34/0x450 [nfnetlink_log]

Acquire the ULOG logger module reference when an ebt_nflog rule is validated and release it when the rule is destroyed. Request the NFLOG backend for legacy callers when needed, matching xt_NFLOG. This prevents module teardown until all ebt_nflog rules have stopped using the logger.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/3bcce49d617c593c7606083bfdb464a1761fa68d
• https://git.kernel.org/stable/c/394d7939c6b2b9e6bea0844c89efb5913168d898
• https://git.kernel.org/stable/c/2cac4294f184c9bc19ff82552c62b80498694c39
• https://git.kernel.org/stable/c/9d8a94b48b393885e7f876c8ef68ed4da5012078
• https://git.kernel.org/stable/c/6809379a860b9fccbb5435bf08343f6d081ac68d
• https://git.kernel.org/stable/c/47a119ec8a7e2d5c8c4e86fb1a56c4e696e500fb
• https://git.kernel.org/stable/c/e2ab7e878bdbe80104c879c31fd2d82a476703b8
• https://git.kernel.org/stable/c/30825970339c107bacaf7f61af90fcdb1f597ca1

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