CVE-2026-26963

Workarounds

There is currently no officially verified or comprehensive workaround for this issue. The following procedure has been validated strictly within a local 'Kind' environment and has not undergone exhaustive testing across diverse production architectures. Proceed with caution.

To mitigate the identified traffic bypass, ensure all ingress traffic from the cilium_wg0 interface is explicitly routed to cilium_host for policy enforcement. This ensures that host-level security policies are applied to decrypted WireGuard traffic. Execute the following configuration on each CiliumNode:

# IPv4 Traffic
ip rule add iif cilium_wg0 table 300
ip route add default dev cilium_host table 300

# IPv6 Traffic
ip -6 rule add iif cilium_wg0 table 300
ip -6 route add default dev cilium_net table 300

Acknowledgements

Special thanks to @julianwiedmann for reporting the issue and helping with the resolution.

For more information

If you think you have found a vulnerability affecting Cilium, we strongly encourage you to report it to our security mailing list at [email protected]. This is a private mailing list for the Cilium security team, and your report will be treated as top priority. Please also address any comments or questions on this advisory to the same mailing list.

Host Policies will incorrectly permit traffic from Pods on other nodes when all of the following configurations are enabled:

• Native Routing
• WireGuard
• Node Encryption (beta)

These options are disabled by default in Cilium.

The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.

CVE-2026-26963 has a CVSS score of 6.1 (Medium). The vector is reachable from an adjacent network, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.18.6); upgrading removes the vulnerable code path.

Kodem intelligence

This issue was fixed by #42892.

This issue affects:

• Cilium v1.18 between v1.18.0 and v1.18.5 inclusive

This issue is fixed in:

• Cilium v1.18.6

1. What is CVE-2026-26963? CVE-2026-26963 is a medium-severity incorrect authorization vulnerability in github.com/cilium/cilium (go), affecting versions >= 1.18.0, < 1.18.5. It is fixed in 1.18.6. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
2. How severe is CVE-2026-26963? CVE-2026-26963 has a CVSS score of 6.1 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/cilium/cilium are affected by CVE-2026-26963? github.com/cilium/cilium (go) versions >= 1.18.0, < 1.18.5 is affected.
4. Is there a fix for CVE-2026-26963? Yes. CVE-2026-26963 is fixed in 1.18.6. Upgrade to this version or later.
5. Is CVE-2026-26963 exploitable, and should I be worried? Whether CVE-2026-26963 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-26963 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-26963? Upgrade github.com/cilium/cilium to 1.18.6 or later.