CVE-2021-43783

Workarounds

This attack is mitigated by restricting access and requiring reviews when registering or modifying scaffolder templates.

For more information

If you have any questions or comments about this advisory:

• Open an issue in the Backstage repository
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A malicious actor with write access to a registered scaffolder template is able to manipulate the template in a way that writes files to arbitrary paths on the scaffolder-backend host instance.

This vulnerability can in some situation also be exploited through user input when executing a template, meaning you do not need write access to the templates. This method will not allow the attacker to control the contents of the injected file however, unless the template is also crafted in a specific way that gives control of the file contents.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2021-43783 has a CVSS score of 8.5 (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 (0.15.14); upgrading removes the vulnerable code path.

Kodem intelligence

This vulnerability is fixed in version 0.15.14 of the @backstage/plugin-scaffolder-backend.

1. What is CVE-2021-43783? CVE-2021-43783 is a high-severity path traversal vulnerability in @backstage/plugin-scaffolder-backend (npm), affecting versions < 0.15.14. It is fixed in 0.15.14. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2021-43783? CVE-2021-43783 has a CVSS score of 8.5 (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-2021-43783? @backstage/plugin-scaffolder-backend (npm) versions < 0.15.14 is affected.
4. Is there a fix for CVE-2021-43783? Yes. CVE-2021-43783 is fixed in 0.15.14. Upgrade to this version or later.
5. Is CVE-2021-43783 exploitable, and should I be worried? Whether CVE-2021-43783 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-2021-43783 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-2021-43783? Upgrade @backstage/plugin-scaffolder-backend to 0.15.14 or later.