CVE-2016-5873 in pecl_http
Summary
by MITRE
Buffer overflow in the HTTP URL parsing functions in pecl_http before 3.0.1 might allow remote attackers to execute arbitrary code via non-printable characters in a URL.
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Analysis
by VulDB Data Team • 05/14/2026
The vulnerability identified as CVE-2016-5873 represents a critical buffer overflow flaw within the pecl_http library version 3.0.0 and earlier. This library serves as a PHP extension for handling HTTP requests and responses, making it a fundamental component in web applications that process HTTP data. The issue specifically manifests in the HTTP URL parsing functions where inadequate input validation allows attackers to craft malicious URLs containing non-printable characters that can trigger memory corruption. The buffer overflow occurs when the library fails to properly handle character sequences that exceed the allocated buffer space during URL parsing operations.
The technical exploitation of this vulnerability leverages the improper handling of URL components through the use of non-printable characters that can bypass standard validation mechanisms. When a malformed URL is processed by the vulnerable library, the parsing functions do not adequately check the length and composition of input data, leading to memory overwrite conditions. This flaw falls under the CWE-121 category of stack-based buffer overflow, where the attacker can manipulate the program execution flow by overwriting stack memory with malicious payloads. The vulnerability is particularly dangerous because it allows remote code execution without requiring authentication or special privileges, making it an attractive target for automated exploitation.
The operational impact of this vulnerability extends beyond simple code execution, as it can lead to complete system compromise when applications using the affected pecl_http library are exposed to malicious HTTP requests. Attackers can leverage this weakness to inject and execute arbitrary code on vulnerable systems, potentially gaining full control over the web server or application hosting environment. The vulnerability affects any PHP application that relies on pecl_http for HTTP processing, including content management systems, web applications, and API gateways that handle user-provided URL data. This makes the attack surface particularly broad across the PHP ecosystem where this extension is commonly deployed.
Mitigation strategies for CVE-2016-5873 involve immediate upgrade to pecl_http version 3.0.1 or later, which includes proper input validation and buffer size checks. Organizations should also implement network-level protections such as web application firewalls that can detect and block malformed URL patterns, particularly those containing non-printable characters. Additionally, input sanitization at the application level should be strengthened to validate all URL parameters before they are processed by the HTTP library. The ATT&CK framework categorizes this vulnerability under T1203 Exploitation for Client Execution, as it represents a remote code execution vector that can be exploited through HTTP-based attack vectors. Regular security assessments and vulnerability scanning should be implemented to identify any remaining instances of the vulnerable library in production environments, while also monitoring for any potential exploitation attempts in network logs and application monitoring systems.