CVE-2026-72421: Linux kernel · ipv4: fib: Don't ignore error route in local/main tables.
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 10.0 Critical · fixed in 5.15.0-1117.124~20.04.1 : patch Linux kernel as a priority.
Data as of 26 Oct 2026, 13:47 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 5.15.0-1117.124~20.04.1, 5.15.0-1123.132~20.04.1, 5.15.0-1122.131~20.04.1 +42
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:NExploitation evidence
Disclosed: evidence found.
CVE published 15 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available to fix this vulnerability. Users should apply the official Linux kernel updates that address this issue. The vendor advisory from Ubuntu confirms that this and other Linux kernel vulnerabilities have been fixed. No additional mitigation steps are required beyond applying the update.
Description
A vulnerability in the Linux kernel's IPv4 fib subsystem was resolved that caused inconsistent behavior in route lookups when CONFIG_IP_MULTIPLE_TABLES is enabled but no rule is added. The fib_lookup() function could overwrite an error route in the merged local/main routing tables with another route from the default table, leading to incorrect routing results. This issue has been fixed to ensure error routes are properly respected.
References
- nvd.nist.gov/vuln/detail/CVE-2026-72421 (opens in a new tab)
- git.kernel.org/stable/c/49eaf1403201357762d745a35882fb734107d763 (opens in a new tab)
- git.kernel.org/stable/c/5ae18d87a45698e8244d0fcba64c658c35a7dd3d (opens in a new tab)
- git.kernel.org/stable/c/828fad4fd418bcdb9f5d66fec0d184c52a85ec31 (opens in a new tab)
- git.kernel.org/stable/c/9127589aabdee588278e8d0d0bd3709a760a92c8 (opens in a new tab)
- git.kernel.org/stable/c/a29e95fbc51e8a1b932773fd0e259b2080881443 (opens in a new tab)
- git.kernel.org/stable/c/a668fa160247d7bbe921548cb845f607b8b9305f (opens in a new tab)
- git.kernel.org/stable/c/b72f0db64205d9ce462038ba995d5d31eff32dc1 (opens in a new tab)
- git.kernel.org/stable/c/fd25996f57a95d56bc568c89b4921edcf334b7d8 (opens in a new tab)
- ubuntu.com/security/CVE-2026-72421 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-72421 (opens in a new tab)
- git.kernel.org/linus/b72f0db64205d9ce462038ba995d5d31eff32dc1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8781-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8876-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8878-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8879-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8877-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8875-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8888-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8889-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-8887-1 (opens in a new tab)