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CVE-2021-21708 : Security Advisory and Response

Discover the impact and mitigation strategies for CVE-2021-21708, a Use After Free vulnerability in PHP versions 7.4.x, 8.0.x, and 8.1.x. Learn about affected systems, exploitation, and prevention.

This CVE-2021-21708 article provides details about a Use After Free (UAF) vulnerability identified in PHP versions 7.4.x, 8.0.x, and 8.1.x. Learn about the impact of the CVE, technical details, and mitigation steps.

Understanding CVE-2021-21708

This section delves into the specifics of the CVE including the vulnerability description, affected systems, exploitation mechanism, and mitigation strategies.

What is CVE-2021-21708?

In PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3, a vulnerability arises when using filter functions with the FILTER_VALIDATE_FLOAT filter and min/max limits. This issue can lead to memory usage after free, potentially causing crashes, memory overwrites, and Remote Code Execution (RCE).

The Impact of CVE-2021-21708

The vulnerability's impact is rated as high, with a CVSS base score of 8.2. It can result in a risk to system integrity and availability without requiring any special user privileges.

Technical Details of CVE-2021-21708

Explore the technical aspects of the vulnerability, including a detailed vulnerability description, affected systems and versions, and the exploitation mechanism used by threat actors.

Vulnerability Description

The vulnerability occurs in code that utilizes FILTER_VALIDATE_FLOAT with minimum and maximum limits, allowing the possibility of memory use after being freed.

Affected Systems and Versions

PHP versions 7.4.x below 7.4.28, 8.0.x below 8.0.16, and 8.1.x below 8.1.3 are affected by this CVE.

Exploitation Mechanism

Threat actors can exploit this vulnerability through crafted requests that trigger the use of memory after it has been deallocated.

Mitigation and Prevention

Learn how to mitigate the risk posed by CVE-2021-21708 by taking immediate steps and implementing long-term security practices.

Immediate Steps to Take

Ensure that affected PHP versions are updated to the patched releases to mitigate the risk of exploitation.

Long-Term Security Practices

Develop secure coding practices, conduct regular security audits, and stay informed about PHP security updates to prevent future vulnerabilities.

Patching and Updates

Regularly apply security patches released by PHP Group to address known vulnerabilities and enhance the security of PHP installations.

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