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CVE-2026-99073: ipv4: stop exception dump when nexthop group shrinks

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-23 · updated 2026-10-23

Description

In the Linux kernel, the following vulnerability has been resolved: ipv4: stop exception dump when nexthop group shrinks Commit 4ce5dc9316de ("inet: switch inet_dump_fib() to RCU protection") allowed IPv4 FIB dumps to run concurrently with nexthop replacement. fib_dump_info_fnhe() uses fib_info_num_path() as the loop bound, then fib_info_nhc() independently reloads nh->nh_grp. If RTM_NEWNEXTHOP replaces a group with fewer paths between those loads, fib_info_nhc() returns NULL and the dump dereferences it through nhc_flags. Stop the walk when the indexed path is absent. Nexthop groups are dense, so the current snapshot has no later path.

Affected products

• Linux kernel: 6.9 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux kernel 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/21cba134c30c17ae55f468b5809336437df5d7e6
• https://git.kernel.org/stable/c/4f4afc07dcb2edd4f9afa36595373f8cdb9b58c2
• https://git.kernel.org/stable/c/b9a30bb7b831e8c5a47fadbdf1760918aaf009cc
• https://git.kernel.org/stable/c/f91e472821e32f58b03eb631e20a67157e2b928b

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