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CVE-2026-72254
netfilter: nft_fib: reject fib expression on the netdev egress hook
Published 2026-08-15 (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-2026-72254 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 | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A fib expression in a netdev egress base chain dereferences nft_in(pkt), NULL on the transmit path, causing a NULL pointer dereference at eval. nft_fib_validate() masks the hook with NF_INET_* values, but netdev hook numbers are a separate enum that aliases them (NF_NETDEV_EGRESS == NF_INET_LOCAL_IN), so an egress chain passes validation and then faults. Add nft_fib_netdev_validate() that limits each result/flag to the netdev hook where the device it reads exists: the input-device cases (OIF, OIFNAME, ADDRTYPE with F_IIF) to ingress, the output-device case (ADDRTYPE with F_OIF) to egress, ADDRTYPE with no device flag to both. Also restrict nft_fib_validate() to NFPROTO_IPV4/IPV6/INET so its NF_INET_* masks are not applied to another family's hooks.
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/nft_fib.c
net/netfilter/nft_fib_netdev.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nft_fib
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NFT_FIB' /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 nft_fibPrints 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_NETFILTER, CONFIG_NFT_FIB
- 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
- 2026-08-15 (2 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.61%, higher than 48.2% 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 |
|---|---|---|
| 5.16 | 6.6.148 | 4fee43759b48 |
| 5.16 | 6.12.101 | 568931f26af4 |
| 5.16 | 6.18.42 | d01c913febea |
| 5.16 | 7.1.5 | f68305267ebd |
| 5.16 | 7.2 | d07955dd34ec |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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:NAttack vector, network
- Once a netdev egress fib rule is installed, evaluation runs on the packet transmit datapath (nf_hook_egress in __dev_queue_xmit); a remote peer can trigger it by causing the host to send matching IPv4/IPv6 traffic through the hooked interface, matching prior netfilter CNA treatment of pre-deployed nftables rules (e.g. CVE-2026-52998).
- AC:LAttack complexity, low
- No race or uncontrollable victim state is required; with an affected egress fib rule present, the attacker reliably triggers the NULL dereference on the next matching outbound packet by controlling protocol headers and normal connection traffic.
- PR:NPrivileges required, none
- Runtime exploitation needs only network traffic through the netdev egress hook; although installing the fib rule requires CAP_NET_ADMIN, validation incorrectly accepts it as legal, so orchestration or administrators can deploy it and remote attackers need no target credentials or local privileges.
- UI:NUser interaction, none
- No victim interaction is required beyond ordinary network traffic processing; the kernel automatically evaluates the fib expression on egress without mounts, file opens, or user prompts.
- S:UScope, unchanged
- Impact is a kernel NULL-pointer fault and host-wide denial of service within the same kernel/network-filtering security authority; it does not constitute VM escape, IOMMU bypass, or another cross-authority boundary change.
- C:NConfidentiality impact, none
- The failure mode is a NULL pointer dereference of nft_in(pkt) on egress (in is NULL in nf_hook_state_init); there is no use-after-free, out-of-bounds read, or other attacker-controlled memory disclosure primitive.
- I:NIntegrity impact, none
- The bug does not corrupt writable memory or provide control-flow hijack; it only dereferences a NULL input device pointer during fib lookup/skipping and cannot modify kernel or user data beyond the immediate fault.
- A:HAvailability impact, high
- The NULL dereference in nft_fib_netdev_eval/nft_fib4_eval/nft_fib6_eval on netdev egress causes a kernel oops/panic-class fault during packet transmission, denying system availability until reboot.