PHP-FPM is a popular server-side scripting language used primarily for web development. It's embedded in web servers and widely deployed across various platforms due to its compatibility and rich feature set. PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with added features useful for heavily loaded sites. It manages the server's request handling, improving PHP performance and resource utilization. Organizations prefer PHP-FPM due to its advanced process management and the ability to handle high loads efficiently. It's particularly popular among web hosting services for its speed and flexibility.
The Remote Code Execution vulnerability in PHP-FPM occurs due to improper handling of the PATH_INFO directive in certain Nginx configurations. This vulnerability, tracked as CVE-2019-11043, allows a remote attacker to execute arbitrary code on the server. The issue arises when a crafted request with an empty PATH_INFO leads to a buffer underflow, enabling code injection. Exploiting this flaw can give attackers significant control over the server environment, allowing unauthorized actions. PHP-FPM versions before 7.1.33, 7.2.x before 7.2.24, and 7.3.x before 7.3.11 are primarily affected.
The vulnerability is triggered when PHP-FPM is used with an Nginx configuration involving the fastcgi_split_path_info directive. An attacker can exploit this by sending a specially crafted request which manipulates PATH_INFO, causing a buffer underflow. The misconfigured server might then execute code contained within the request. Key elements involved include the directive handling logic and the input validation processes. The crafted requests exploit known endpoints typically leveraging scripts like index.php, combined with malicious headers.
Exploitation of this vulnerability could potentially lead to a complete server compromise. Malicious actors could execute arbitrary commands on the server, escalate privileges, exfiltrate sensitive data, or disrupt services. The impact of successful exploitation extends to service downtime, data breaches, and loss of confidentiality, integrity, and availability. It poses significant security risks, particularly to sites or services dependent on PHP and Nginx with incorrect configurations.
REFERENCES
- Upgrade PHP to versions 7.1.33, 7.2.24, 7.3.11 or later.
- Remove the fastcgi_split_path_info directive from Nginx configurations.
- Ensure proper validation of PATH_INFO in server configurations.
- Regularly update and patch software components to mitigate known vulnerabilities.
- Conduct security assessments and incorporate configuration checks.
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