Generator Web Application: Local Privilege Escalation Vulnerability via System Temp Directory
Published: 2021-03-11T03:09:16Z
Aliases: CVE-2021-21363

### Impact

On Unix like systems, the system's temporary directory is shared between all users on that system. A collocated user can observe the process of creating a temporary sub directory in the shared temporary directory and race to complete the creation of the temporary subdirectory. 

This vulnerability is local privilege escalation because the contents of the `outputFolder` can be appended to by an attacker. As such, code written to this directory, when executed can be attacker controlled.

#### Java Code

The method `File.createTempFile` from the JDK is vulnerable to this local information disclosure vulnerability.

https://github.com/swagger-api/swagger-codegen/blob/068b1ebcb7b04a48ad38f1cadd24bb3810c9f1ab/modules/swagger-generator/src/main/java/io/swagger/generator/online/Generator.java#L174-L185


### Patches

Fix has been applied to the master branch with:

* https://github.com/swagger-api/swagger-codegen/commit/987ea7a30b463cc239580d6ad166c707ae942a89

included in release: 2.4.19


### References

* [CWE-378: Creation of Temporary File With Insecure Permissions](https://cwe.mitre.org/data/definitions/378.html)
* [CWE-379: Creation of Temporary File in Directory with Insecure Permissions](https://cwe.mitre.org/data/definitions/379.html)

### For more information
If you have any questions or comments about this advisory:

* Email us at [security@swagger.io](mailto:security@swagger.io)

#### Original vulnerability report

> I'm performing OSS security research under the GitHub Security Lab Bug Bounty program.
> I've been using a custom CodeQL query to find local temporary directory vulnerabilities in OSS with three custom CodeQL queries.
> 
> - https://github.com/github/codeql/pull/4388/files#diff-71d36c0f2bd0b08e32866f873f1c906cdc17277e0ad327c0c6cd2c882f30de4f
> - https://github.com/github/codeql/pull/4388/files#diff-1893a18a8bf43c011d61a7889d0139b998a5a78701a30fe7722eddd4c506aaac
> - https://github.com/github/codeql/pull/4473
> 
> The code generated by the Swagger Generator contains a local information disclosure vulnerability. The system temporary directory, on unix-like systems is shared between multiple users. Information written to this directory, or directories created under this directory that do not correctly set the posix standard permissions can have these directories read/modified by other users.
> 
> ---
> 
> This vulnerability exists in the maven plugin.
> 
> This vulnerability is distinctly different. This vulnerability is most likely a local privilege escalation vulnerability.
> 
> https://github.com/swagger-api/swagger-codegen/blob/068b1ebcb7b04a48ad38f1cadd24bb3810c9f1ab/modules/swagger-generator/src/main/java/io/swagger/generator/online/Generator.java#L174-L185
> 
> This vulnerability is very similar to this similar vulnerability I disclosed in the Eclipse Jetty project.
> 
> https://github.com/eclipse/jetty.project/security/advisories/GHSA-g3wg-6mcf-8jj6
> 
> This is due to a race condition between the call to `delete` and the call to `mkdirs`.
> 
> ```java
> // ensure file will always be unique by appending random digits
> File outputFolder = File.createTempFile("codegen-", "-tmp"); // Attacker knows the full path of the file that will be generated
> // delete the file that was created
> outputFolder.delete(); // Attacker sees file is deleted and begins a race to create their own directory before Swagger Code Generator.
> // and make a directory of the same name
> // SECURITY VULNERABILITY: Race Condition! - Attacker beats Swagger Code Generator and now owns this directory
> outputFolder.mkdirs();
> ```
> 
> This vulnerability is local privilege escalation because the contents of the `outputFolder` can be appended to by an attacker. As such, code written to this directory, when executed can be attacker controlled.
> 
> The fix here is to switch to the `Files` API for creating temporary directories. Which does not contain this race condition, and appropriately sets the correct file permissions.
>