CVE-2020-15250 in Banking Liquidity Management
Summary
by MITRE • 10/13/2020
In JUnit4 from version 4.7 and before 4.13.1, the test rule TemporaryFolder contains a local information disclosure vulnerability. 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. This vulnerability impacts you if the JUnit tests write sensitive information, like API keys or passwords, into the temporary folder, and the JUnit tests execute in an environment where the OS has other untrusted users. 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. For Java 1.7 and higher users: this vulnerability is fixed in 4.13.1. For Java 1.6 and lower users: no patch is available, you must use the workaround below. 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. For more information, including an example of vulnerable code, see the referenced GitHub Security Advisory.
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Analysis
by VulDB Data Team • 10/24/2025
The vulnerability described in CVE-2020-15250 affects the JUnit4 testing framework, specifically within the TemporaryFolder test rule implementation. This issue represents a local information disclosure vulnerability that exists in versions 4.7 through 4.13.0 of JUnit4, creating a security risk on Unix-like operating systems where the system temporary directory is shared among all users. The fundamental flaw stems from the default file permissions applied to temporary files and directories created within this shared space, which by default are readable by all users on the system. This vulnerability is categorized under CWE-200 as it involves the improper exposure of information to unauthorized users, and aligns with ATT&CK technique T1005 for data from local system repositories.
The technical implementation of this vulnerability occurs when JUnit tests utilize the TemporaryFolder rule to store sensitive data such as API keys, passwords, or other confidential information within the system's temporary directory. On Unix-like systems, the /tmp directory or equivalent shared temporary space is typically created with world-readable permissions, meaning that any user on the system can access files created by other users. While this vulnerability does not permit direct modification or overwriting of the temporary files by unauthorized users, it does enable information disclosure that could compromise sensitive test data. The vulnerability is particularly concerning because it operates at the file system level rather than through network protocols or application-level flaws, making it a persistent risk in multi-user environments where security isolation is expected.
The operational impact of this vulnerability extends beyond simple data exposure, as it creates a vector for potential privilege escalation and lateral movement within compromised systems. Attackers with access to the same system can exploit this weakness to gather sensitive information that may have been inadvertently stored in temporary files during test execution. This risk is particularly significant in environments where multiple users share the same system or when JUnit tests are executed with elevated privileges. The vulnerability affects the security posture of applications that rely on JUnit4 for testing, as it could expose sensitive information that might otherwise remain protected within properly secured temporary storage areas. Organizations using older Java versions, specifically Java 1.6 and below, face additional challenges since the standard fix is not available for those environments, requiring alternative workarounds.
The mitigation strategies for this vulnerability depend on the Java runtime environment being used. For users operating on Java 1.7 or higher, upgrading to JUnit4 version 4.13.1 resolves the issue through improved file system handling and permission management. However, for Java 1.6 and lower users who cannot upgrade, the recommended workaround involves explicitly setting the java.io.tmpdir system property to point to a directory exclusively owned by the executing user. This approach ensures that temporary files are created in a location with appropriate access controls, preventing unauthorized users from reading the temporary files. The fix demonstrates compliance with security best practices by ensuring that sensitive temporary data is properly isolated and protected from unauthorized access, aligning with principles found in the OWASP Top Ten and NIST cybersecurity frameworks. Organizations should also consider implementing additional monitoring and logging of temporary file creation activities to detect potential exploitation attempts.