JUnit4 test rule TemporaryFolder contains a local information disclosure vulnerability (Low Severity)

[kristovatlas]

Remediation
Upgrade junit:junit to version 4.13.1 or later. For example:

junit junit [4.13.1,) Always verify the validity and compatibility of suggestions with your codebase.

Details
GHSA-269g-pwp5-87pp
low severity
Vulnerable versions: >= 4.7, < 4.13.1
Patched version: 4.13.1
Vulnerability
The JUnit4 test rule TemporaryFolder contains a local information disclosure vulnerability.

Example of vulnerable code:

public static class HasTempFolder {
@rule
public TemporaryFolder folder = new TemporaryFolder();

@Test
public void testUsingTempFolder() throws IOException {
    folder.getRoot(); // Previous file permissions: `drwxr-xr-x`; After fix:`drwx------`
    File createdFile= folder.newFile("myfile.txt"); // unchanged/irrelevant file permissions
    File createdFolder= folder.newFolder("subfolder"); // unchanged/irrelevant file permissions
    // ...
}

}
Impact
On Unix like systems, the system's temporary directory is shared between all users on that system. Because of this, when files and directories are written into this directory they are, by default, readable by other users on that same system.

This vulnerability does not allow other users to overwrite the contents of these directories or files. This is purely an information disclosure vulnerability.

When analyzing the impact of this vulnerability, here are the important questions to ask:

Do the JUnit tests write sensitive information, like API keys or passwords, into the temporary folder?
If yes, this vulnerability impacts you, but only if you also answer 'yes' to question 2.
If no, this vulnerability does not impact you.
Do the JUnit tests ever execute in an environment where the OS has other untrusted users.
This may apply in CI/CD environments but normally won't be 'yes' for personal developer machines.
If yes, and you answered 'yes' to question 1, this vulnerability impacts you.
If no, this vulnerability does not impact you.
Patches
Because certain JDK file system APIs were only added in JDK 1.7, this this fix is dependent upon the version of the JDK you are using.

Java 1.7 and higher users: this vulnerability is fixed in 4.13.1.
Java 1.6 and lower users: no patch is available, you must use the workaround below.
Workarounds
If you are unable to patch, or are stuck running on Java 1.6, specifying the java.io.tmpdir system environment variable to a directory that is exclusively owned by the executing user will fix this vulnerability.

References
CWE-200: Exposure of Sensitive Information to an Unauthorized Actor
Fix commit junit-team/junit4@610155b
Similar Vulnerabilities
Google Guava - google/guava#4011
Apache Ant - https://nvd.nist.gov/vuln/detail/CVE-2020-1945
JetBrains Kotlin Compiler - https://nvd.nist.gov/vuln/detail/CVE-2020-15824
For more information
If you have any questions or comments about this advisory, please pen an issue in junit-team/junit4.