Bug 2516308 (CVE-2026-72254)

Summary: CVE-2026-72254 kernel: netfilter: nft_fib: reject fib expression on the netdev egress hook
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: low    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `netfilter` subsystem. A local attacker could exploit a vulnerability where a `fib` expression in a `netdev egress base chain` incorrectly dereferences a NULL pointer. This can lead to a NULL pointer dereference, causing a system crash and resulting in a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-08-15 06:05:41 UTC 
In the Linux kernel, the following vulnerability has been resolved:

netfilter: nft_fib: reject fib expression on the netdev egress hook

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.
Comment 1 Keith Grant 2026-08-18 17:37:30 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081553-CVE-2026-72254-fb72@gregkh/T