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CVE-2026-74660
netfilter: ebt_nflog: pin the NFLOG backend
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem net/bridge. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74660 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 | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. 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
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.
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/bridge/netfilter/ebt_nflog.c
- What this is
- NETFILTERMAINTAINERS section matched on net/*/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- ebt_nflog
Check it on the machine
grep -wE 'CONFIG_BRIDGE|CONFIG_BRIDGE_EBT_NFLOG|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 ebt_nflogPrints 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_BRIDGE, CONFIG_BRIDGE_EBT_NFLOG, 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
- 2026-08-22 (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
- 0.13%, higher than 2.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/bridge
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.12 | 5.10.265 | 3bcce49d617c |
| 4.12 | 5.15.216 | 394d7939c6b2 |
| 4.12 | 6.1.183 | 2cac4294f184 |
| 4.12 | 6.6.152 | 9d8a94b48b39 |
| 4.12 | 6.12.104 | 6809379a860b |
| 4.12 | 6.18.45 | 47a119ec8a7e |
| 4.12 | 7.1.9 | e2ab7e878bdb |
| 4.12 | 7.2 | 30825970339c |
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 |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | 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 UAF is reached through ebtables setsockopt rule installation and nfnetlink_log module teardown (local administrative paths); per kernel CNA guidance, netfilter/ebtables bugs are scored Local even when bridge hook evaluation can be driven by forwarded frames.
- AC:LAttack complexity, low
- The KASAN reproducer uses a deterministic two-thread race between nfnetlink_log_fini() module removal and concurrent bridge traffic through an active ebt_nflog rule; the attacker controls both the unload timing and packet generation without depending on uncontrollable victim state.
- PR:LPrivileges required, low
- Installing an ebt_nflog rule requires CAP_NET_ADMIN in the socket network namespace, obtainable by unprivileged users via user+network namespaces (unshare -Urn); the documented PoC races module teardown concurrently with rule-driven traffic, matching standard CNA treatment for ebtables/netfilter paths.
- UI:NUser interaction, none
- No victim interaction is required beyond the attacker's own ebtables configuration, module unload coordination, and bridge traffic generation to hit the active nflog target during the teardown window.
- S:UScope, unchanged
- The slab use-after-free corrupts host kernel memory within the same security authority; this is not a VM escape, container breakout across an IOMMU boundary, or other cross-scope privilege transition.
- C:HConfidentiality impact, high
- KASAN confirmed a slab use-after-free read in instance_lookup_get_rcu() against freed nfnl_log_pernet state; UAF on the per-net instance hash table enables attacker-influenced heap reads and disclosure of adjacent kernel memory contents.
- I:HIntegrity impact, high
- Use-after-free on the nfnl_log_pernet structure and nfulnl_instance objects provides standard heap grooming primitives; freed slab reuse can redirect subsequent logging operations into attacker-controlled data for arbitrary kernel writes or control-flow hijack.
- A:HAvailability impact, high
- The UAF read on freed per-net logging state can immediately trigger a kernel BUG/oops (as reported by KASAN) and reliably causes denial of service; repeated bridge traffic during module teardown can panic the affected host.