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CVE-2026-99071: ipv4: do not warn on route notification size race

• 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: do not warn on route notification size race Commit 680aea08e78c ("net: ipv4: Emit notification when fib hardware flags are changed") added asynchronous route notifications for hardware flag changes. fib_alias_hw_flags_set() sizes the skb with fib_nlmsg_size() and later fills it with fib_dump_info() while holding only RCU. With nexthop compatibility mode enabled, a concurrent replacement can grow the group between these independent snapshots. fib_dump_info() can then legitimately return -EMSGSIZE, so the warning does not prove a sizing bug. Remove the warning. The existing error path still frees the skb and reports the error to listeners.

Affected products

• Linux kernel: 5.12 — 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/088ba80eef85fa7a5ad8f9e7c82b403c99242b56
• https://git.kernel.org/stable/c/221ef5e1e44a044790f0f54e6aa237883f475a4d
• https://git.kernel.org/stable/c/78a1cf5c54b2f795c81fedb530755a8d01cc84f0
• https://git.kernel.org/stable/c/7dfa7ca97f3ac46353edd4cc44f7733758e4535b
• https://git.kernel.org/stable/c/e02a5b6588161673ef75a4bc5cdfb62bd493374d

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