Summary
CiliumLocalRedirectPolicy addressMatcher allows cross-namespace service traffic hijacking and can break service translation
Full technical description
Workarounds
There is no workaround to this issue.
Acknowledgements
The Cilium community has worked together with members of Isovalent to prepare these mitigations. Special thanks to @ysksuzuki for investigating and fixing the issue.
For more information
If there are any questions or comments about this advisory, please reach out on Slack.
To report potential vulnerabilities affecting Cilium, it strongly is encouraged to report them through the security mailing list at [email protected]. This is a private mailing list for the Cilium security team, and reports will be treated as a top priority.
Impact
Users with the ability to create CiliumLocalRedirectPolicies can specify arbitrary ClusterIPs via addressMatcher, which enables hijacking traffic to Services in any namespace, bypassing the namespace-scoping guarantees enforced by serviceMatcher.
In addition, deleting such a policy can corrupt Cilium's internal service state, causing service translation to stop working entirely for the affected Service.
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
CVE-2026-53935 has a CVSS score of 6.9 (Medium). The vector is reachable from an adjacent network, high 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 (1.19.4, 1.18.10, 1.17.16); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
This issue affects:
- Cilium v1.19.0 to v1.19.3 inclusive (fixed in PR #45584)
- Cilium v1.18.2 to v1.18.9 inclusive (fixed in PR #45585)
- All versions of Cilium prior to v1.17.16 (fixed in PR #45412)
This issue has been patched in:
- Cilium v1.19.4
- Cilium v1.18.10
- Cilium v1.17.16
Frequently Asked Questions
- What is CVE-2026-53935? CVE-2026-53935 is a medium-severity open redirect vulnerability in github.com/cilium/cilium (go), affecting versions >= 1.19.0, < 1.19.4. It is fixed in 1.19.4, 1.18.10, 1.17.16. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- How severe is CVE-2026-53935? CVE-2026-53935 has a CVSS score of 6.9 (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.
- Which versions of github.com/cilium/cilium are affected by CVE-2026-53935? github.com/cilium/cilium (go) versions >= 1.19.0, < 1.19.4 is affected.
- Is there a fix for CVE-2026-53935? Yes. CVE-2026-53935 is fixed in 1.19.4, 1.18.10, 1.17.16. Upgrade to this version or later.
- Is CVE-2026-53935 exploitable, and should I be worried? Whether CVE-2026-53935 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
- What actually determines whether CVE-2026-53935 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.
- How do I fix CVE-2026-53935?
- Upgrade
github.com/cilium/ciliumto 1.19.4 or later - Upgrade
github.com/cilium/ciliumto 1.18.10 or later - Upgrade
github.com/cilium/ciliumto 1.17.16 or later
- Upgrade