CVE-2026-72421: ipv4: fib: Don't ignore error route in local/main tables.
In the Linux kernel, the following vulnerability has been resolved:
ipv4: fib: Don't ignore error route in local/main tables.
When CONFIGIPMULTIPLETABLES is enabled but no rule is added, fiblookup() performs route lookup directly on two tables.
Since the first lookup does not properly bail out, the result of an error route in the merged local/main table could be overwritten by another route in the default table:
# unshare -n # ip link set lo up # ip route add 192.168.0.0/24 dev lo table 253 # ip route add unreachable 192.168.0.0/24 # ip route get 192.168.0.1 192.168.0.1 dev lo table default uid 0 cache <local>
Once a random rule is added, the error route is respected:
# ip rule add table 0 # ip rule del table 0 # ip route get 192.168.0.1 RTNETLINK answers: No route to host
Let's fix the inconsistent behaviour.
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-72421?
CVE-2026-72421 has a risk rating of 15, indicating a high severity vulnerability.
How do I fix CVE-2026-72421?
To address CVE-2026-72421, ensure that you update the Linux kernel to the latest patched version.
What systems are affected by CVE-2026-72421?
CVE-2026-72421 affects systems running the Linux kernel with CONFIG_IP_MULTIPLE_TABLES enabled.
What is the main issue described in CVE-2026-72421?
The main issue in CVE-2026-72421 is that fib_lookup() in the Linux kernel does not handle error routes correctly when no rules are added.
When was CVE-2026-72421 published?
CVE-2026-72421 was published on August 15, 2026.