CVE-2021-21430

Creation of Temporary File in Directory with Insecure Permissions in auto-generated Java, Scala code

For more information

If you have any questions or comments about this advisory:

• Open an issue in OpenAPI Generator Github repo
• Email us at [email protected]

This vulnerability impacts generated code. If this code was generated as a one-off occasion, not as a part of an automated CI/CD process, this code will remain vulnerable until fixed manually!

On Unix-Like systems, the system temporary directory is shared between all local users. When files/directories are created, the default umask settings for the process are respected. As a result, by default, most processes/apis will create files/directories with the permissions -rw-r--r-- and drwxr-xr-x respectively, unless an API that explicitly sets safe file permissions is used.

This vulnerability exists due to the use of the JDK method File.createTempFile. This method creates an insecure temporary files that can leave application and system data vulnerable to exposure.

Auto-generated code (Java, Scala) that deals with uploading or downloading binary data through API endpoints will create insecure temporary files during the process. For example, if the API endpoint returns a PDF file, the auto-generated clients will first download the PDF into a insecure temporary file that can be read by anyone on the system.

Affected generators:

• Java
  • okhttp-gson (default library)
    https://github.com/OpenAPITools/openapi-generator/blob/d85f61ff0cfd6b8cd7063a63f302998a51466269/modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/ApiClient.mustache#L1085-L1088
  • jersey2
    https://github.com/OpenAPITools/openapi-generator/blob/d85f61ff0cfd6b8cd7063a63f302998a51466269/modules/openapi-generator/src/main/resources/Java/libraries/jersey2/ApiClient.mustache#L1035-L1038
  • resteasy
    https://github.com/OpenAPITools/openapi-generator/blob/d85f61ff0cfd6b8cd7063a63f302998a51466269/modules/openapi-generator/src/main/resources/Java/libraries/resteasy/ApiClient.mustache#L604-L607
  • retrofit2
    https://github.com/OpenAPITools/openapi-generator/blob/d85f61ff0cfd6b8cd7063a63f302998a51466269/modules/openapi-generator/src/main/resources/Java/libraries/retrofit2/play26/ApiClient.mustache#L202-L208
• Scala
  • scala-finch
    https://github.com/OpenAPITools/openapi-generator/blob/764a3b044c19fadf4a0789473cde96a65b77868a/modules/openapi-generator/src/main/resources/scala-finch/api.mustache#L83-L88
  • scala-akka
    https://github.com/OpenAPITools/openapi-generator/blob/150e24dc553a8ea5230ffb938ed3e6020e972faa/modules/openapi-generator/src/main/resources/scala-akka-http-server/multipartDirectives.mustache#L71-L73

The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access. Typical impact: privilege escalation beyond the intended level.

CVE-2021-21430 has a CVSS score of 6.2 (Medium). The vector is requires local access, 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 (5.1.0); upgrading removes the vulnerable code path.

Kodem intelligence

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The issue has been patched by changing the generated code to use the JDK method Files.createTempFile and released in the v5.1.0 stable version.

This vulnerability has the same root cause as CVE-2021-21364 from the swagger-api/swagger-codegen project as this project and that one both share the same original source tree.
https://github.com/swagger-api/swagger-codegen/security/advisories/GHSA-hpv8-9rq5-hq7w

1. What is CVE-2021-21430? CVE-2021-21430 is a medium-severity improper privilege management vulnerability in org.openapitools:openapi-generator (maven), affecting versions < 5.1.0. It is fixed in 5.1.0. The application assigns, modifies, tracks, or checks privileges incorrectly, allowing a user to gain elevated access.
2. How severe is CVE-2021-21430? CVE-2021-21430 has a CVSS score of 6.2 (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 org.openapitools:openapi-generator are affected by CVE-2021-21430? org.openapitools:openapi-generator (maven) versions < 5.1.0 is affected.
4. Is there a fix for CVE-2021-21430? Yes. CVE-2021-21430 is fixed in 5.1.0. Upgrade to this version or later.
5. Is CVE-2021-21430 exploitable, and should I be worried? Whether CVE-2021-21430 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-2021-21430 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-2021-21430? Upgrade org.openapitools:openapi-generator to 5.1.0 or later.

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