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CVE-2026-72421

10.0 · CRITICAL

In the Linux kernel, the following vulnerability has been resolved: ipv4: fib: Don't ignore error route in local/main tables.

Published Aug 15, 2026EPSS 0.60%

Overview

CVE-2026-72421 is a critical-severity vulnerability. It was published on August 15, 2026 and has a CVSS 3.1 base score of 10.0 (CRITICAL).

This vulnerability has a CVSS 3.1 base score of 10.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refgit.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763Refgit.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3dRefgit.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31Refgit.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8Refgit.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443Refgit.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305fRefgit.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1Refgit.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8

How CyberStrike helps

Frequently asked questions

What is CVE-2026-72421?

CVE-2026-72421 is a critical-severity vulnerability. It was published on August 15, 2026 and has a CVSS 3.1 base score of 10.0 (CRITICAL).

How severe is CVE-2026-72421?

This vulnerability has a CVSS 3.1 base score of 10.0, rated CRITICAL. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-72421?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-72421?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-72421 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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