CVE-2023-27595

Workarounds

There are no known workarounds.

Acknowledgements

The Cilium community has worked together with members of Isovalent to prepare these mitigations. Special thanks to Louis DeLosSantos and Timo Beckers for investigating and fixing the issue.

For more information

If you have any questions or comments about this advisory, please reach out on Slack.

As usual, if you think you found a related vulnerability, we strongly encourage you to report security vulnerabilities to our private security mailing list: [email protected] - first, before disclosing them in any public forums. This is a private mailing list where only members of the Cilium internal security team are subscribed to, and is treated as top priority.

When Cilium is started, there is a short period when Cilium eBPF programs are not attached to the host. During this period, the host does not implement any of Cilium's featureset. This can cause disruption to newly established connections during this period due to the lack of Load Balancing, or can cause Network Policy bypass due to the lack of Network Policy enforcement during the window. This vulnerability impacts any Cilium-managed endpoints on the node (such as Kubernetes Pods), as well as the host network namespace (including Host Firewall).

CVE-2023-27595 has a CVSS score of 6.5 (Medium). The vector is network-reachable, 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 (1.13.1); upgrading removes the vulnerable code path.

Kodem intelligence

This vulnerability is fixed by https://github.com/cilium/cilium/pull/24336, included in Cilium 1.13.1 or later. Cilium releases 1.12.x, 1.11.x and earlier are not affected.

1. What is CVE-2023-27595? CVE-2023-27595 is a medium-severity security vulnerability in github.com/cilium/cilium (go), affecting versions >= 1.13.0, < 1.13.1. It is fixed in 1.13.1.
2. How severe is CVE-2023-27595? CVE-2023-27595 has a CVSS score of 6.5 (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-2023-27595? github.com/cilium/cilium (go) versions >= 1.13.0, < 1.13.1 is affected.
4. Is there a fix for CVE-2023-27595? Yes. CVE-2023-27595 is fixed in 1.13.1. Upgrade to this version or later.
5. Is CVE-2023-27595 exploitable, and should I be worried? Whether CVE-2023-27595 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-2023-27595 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-2023-27595? Upgrade github.com/cilium/cilium to 1.13.1 or later.