CVE-2021-23521 Explained : Impact and Mitigation

This CVE, titled 'Link Following', was made public on January 31, 2022, affecting the JUCE package before version 6.1.5. The vulnerability allows for the crafting of a malicious archive with a symbolic link entry that, when extracted, can lead to writing arbitrary files on the target host and potentially enable an attacker to execute unauthorized code.

Understanding CVE-2021-23521

This section will delve into the details of CVE-2021-23521, explaining the vulnerability, its impact, affected systems, and how to prevent exploitation.

What is CVE-2021-23521?

CVE-2021-23521 affects the JUCE package before version 6.1.5, triggered by a crafted malicious archive entry. It allows for the traversal of symbolic links outside the target directory, leading to the writing of unauthorized files and potential execution of arbitrary code.

The Impact of CVE-2021-23521

The vulnerability presents a medium severity threat with a CVSS base score of 5.5. It has a low attack complexity and vector, high confidentiality impact, and low privileges required. The impact includes unauthorized file writing and potential execution of arbitrary code on the target host.

Technical Details of CVE-2021-23521

In this section, we will explore the technical aspects of CVE-2021-23521, including vulnerability description, affected systems and versions, and the exploitation mechanism.

Vulnerability Description

The vulnerable code lies in the ZipFile::uncompressEntry function in juce_ZipFile.cpp. It is executed during the extraction of an archive when uncompressTo() is called on a ZipFile object, allowing the traversal of symbolic links outside the intended target directory.

Affected Systems and Versions

The vulnerability impacts the JUCE package versions before 6.1.5, exposing systems that utilize these vulnerable versions to potential exploitation through crafted malicious archives.

Exploitation Mechanism

By creating a malicious archive with a symbolic link entry and extracting it using the ZipFile object's uncompressTo() function, an attacker can traverse symbolic links outside the target directory, writing unauthorized files and possibly executing arbitrary code.

Mitigation and Prevention

To protect systems from CVE-2021-23521, immediate steps need to be taken, and long-term security practices should be implemented to ensure ongoing protection against similar vulnerabilities.

Immediate Steps to Take

System administrators and users are advised to update the JUCE package to version 6.1.5 or above immediately to prevent exploitation of this vulnerability. Additionally, exercise caution when handling unknown or untrusted archives.

Long-Term Security Practices

In the long term, maintain regular monitoring and updating of software components, utilize secure coding practices, and conduct security assessments to identify and address potential vulnerabilities proactively.

Patching and Updates

Stay informed about security patches and updates released by JUCE for the package to address known vulnerabilities and improve the overall security posture of systems.