In the Linux kernel, the following vulnerability has been resolved: ipv4: fib: Don't ignore error route in local/main tables.
CVE-2026-72421 · published 15 Aug 2026
How serious is it
- Severity: critical, CVSS score 10 out of 10.
- No exploit prediction (EPSS) score yet.
- Not on the CISA list of exploited vulnerabilities.
- No public exploit in Exploit-DB.
Is your app affected by CVE-2026-72421?
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Who is affected
- Linux Linux: 3.6
How to check
- Find out whether you run the affected product and which version, then compare it with the versions above.
How to fix
Copies a prompt for Claude Code, Cursor or Codex that asks it to check whether you run this product.
- Apply the vendor's update or mitigation from the references below. If there is none yet, limit exposure of the affected service until there is.
- If a vulnerable version was live, check your logs and rotate the secrets that server could read.
The advisory
In the Linux kernel, the following vulnerability has been resolved:
ipv4: fib: Don't ignore error route in local/main tables.
When CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added,
fib_lookup() 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.
Check your whole app
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References
- git.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763
- git.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3d
- git.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31
- git.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8
- git.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443
- git.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305f
- git.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1
- git.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8
Merged from NVD. Last updated 23 Oct 2026. All vulnerabilities · RSS · JSON