CVE-2026-72421

Received Received - Intake

Improper route handling in Linux kernel

Publication date: 2026-08-15

Last updated on: 2026-08-17

Assigner: kernel.org

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.

CVSS Scores

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Meta Information

Published

2026-08-15

Last Modified

2026-08-17

Generated

2026-09-04

AI Q&A

2026-08-15

EPSS Evaluated

2026-09-03

NVD

CVE-2026-72421

EUVD

EUVD-2026-59320

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel occurs when CONFIG_IP_MULTIPLE_TABLES is enabled but no routing rule is added. The fib_lookup() function performs route lookups on local and main tables. If the first lookup fails to handle an error route properly, a valid route in the default table can overwrite the error route, leading to incorrect routing behavior.

Detection Guidance

To detect this vulnerability, check if CONFIG_IP_MULTIPLE_TABLES is enabled in your kernel and verify if error routes in local/main tables are being ignored. Run: uname -a to check kernel version, grep CONFIG_IP_MULTIPLE_TABLES /boot/config-$(uname -r) to confirm the config, and ip route get 192.168.0.1 to test route lookup behavior.

Impact Analysis

This vulnerability could cause network traffic to be incorrectly routed or blocked. For example, a system might fail to properly handle unreachable routes, leading to unexpected connection failures or misrouted packets. This could disrupt network services or applications relying on specific routing rules.

Compliance Impact

This vulnerability affects network routing in the Linux kernel, which could lead to unauthorized network access or data exfiltration. For GDPR, it may impact data protection by enabling unauthorized data transmission. For HIPAA, it could compromise protected health information confidentiality by allowing unauthorized network routes.

Mitigation Strategies

Apply the latest kernel update to patch this issue. If immediate patching is not possible, add a dummy rule to enforce proper route lookup: ip rule add table 0 followed by ip rule del table 0. Ensure CONFIG_IP_MULTIPLE_TABLES is properly configured.

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