CVE-2023-35926

The Backstage scaffolder-backend plugin uses a templating library that requires a sandbox, as it by design allows for code injection. The library used for this sandbox so far has been vm2, but in light of several past vulnerabilities and existing vulnerabilities that may not have a fix, the plugin has switched to using a different sandbox library.

Workarounds

Note that the Backstage Threat Model states that scaffolder templates are considered to be a sensitive area that with the recommendation that you control access and perform manual reviews of changes to the scaffolder templates. The exploit is of a nature where it is easily discoverable in manual review.

A malicious actor with write access to a registered scaffolder template could manipulate the template in a way that allows for remote code execution on the scaffolder-backend instance. This was only exploitable in the template YAML definition itself and not by user input data.

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-2023-35926 has a CVSS score of 8.0 (High). The vector is network-reachable, 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 (1.15.0); upgrading removes the vulnerable code path.

Kodem intelligence

This is vulnerability is fixed in version 1.15.0 of @backstage/plugin-scaffolder-backend.

1. What is CVE-2023-35926? CVE-2023-35926 is a high-severity code injection vulnerability in @backstage/plugin-scaffolder-backend (npm), affecting versions < 1.15.0. It is fixed in 1.15.0. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2023-35926? CVE-2023-35926 has a CVSS score of 8.0 (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 @backstage/plugin-scaffolder-backend are affected by CVE-2023-35926? @backstage/plugin-scaffolder-backend (npm) versions < 1.15.0 is affected.
4. Is there a fix for CVE-2023-35926? Yes. CVE-2023-35926 is fixed in 1.15.0. Upgrade to this version or later.
5. Is CVE-2023-35926 exploitable, and should I be worried? Whether CVE-2023-35926 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-2023-35926 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-2023-35926? Upgrade @backstage/plugin-scaffolder-backend to 1.15.0 or later.