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CVE-2021-21703 : Security Advisory and Response

Get insights on CVE-2021-21703 where PHP versions 7.3.x up to 7.3.31, 7.4.x below 7.4.25, and 8.0.x below 8.0.12 are impacted by a PHP-FPM memory access vulnerability leading to privilege escalation.

PHP-FPM memory access vulnerability in PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25, and 8.0.x below 8.0.12 could allow local unprivileged users to escalate privileges to root due to memory access in the root process.

Understanding CVE-2021-21703

PHP-FPM memory access vulnerability impacting PHP versions leading to potential privilege escalation.

What is CVE-2021-21703?

In PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25, and 8.0.x below 8.0.12, a vulnerability in the PHP-FPM SAPI can be exploited by child processes to access and modify the memory shared with the main process, enabling unauthorized privilege escalation.

The Impact of CVE-2021-21703

The vulnerability allows local unprivileged users to access memory shared with the main PHP-FPM process, potentially leading to unauthorized modification of the memory and escalating privileges to the root user.

Technical Details of CVE-2021-21703

PHP versions 7.3.x up to and including 7.3.31, 7.4.x below 7.4.25, and 8.0.x below 8.0.12 in PHP-FPM SAPI allow child worker processes to interact with and modify memory shared with the main FPM daemon process, leading to potential privilege escalation.

Vulnerability Description

Child processes in PHP-FPM can access memory shared with the root process, enabling unauthorized modifications that could be leveraged to escalate privileges from local unprivileged users to the root user.

Affected Systems and Versions

PHP versions 7.3.x, 7.4.x, and 8.0.x are affected, specifically up to and including PHP 7.3.31, below 7.4.25, and below 8.0.12.

Exploitation Mechanism

By exploiting the memory access capabilities of PHP-FPM child processes, attackers can manipulate shared memory to potentially gain root privileges.

Mitigation and Prevention

Taking immediate action to mitigate the risk of privilege escalation through the PHP-FPM memory access vulnerability is crucial.

Immediate Steps to Take

Update PHP to versions 7.3.32, 7.4.26, or 8.0.13 to address the vulnerability and prevent unauthorized privilege escalation.

Long-Term Security Practices

Ensure PHP-FPM is configured securely, with appropriate process privileges to restrict access and prevent unauthorized memory modifications.

Patching and Updates

Regularly monitor PHP security advisories and apply patches promptly to mitigate known vulnerabilities and enhance the overall security posture of PHP installations.

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