CVE-2016-5385 in Communications BRM
Summary
by MITRE
PHP through 7.0.8 does not attempt to address RFC 3875 section 4.1.18 namespace conflicts and therefore does not protect applications from the presence of untrusted client data in the HTTP_PROXY environment variable, which might allow remote attackers to redirect an application's outbound HTTP traffic to an arbitrary proxy server via a crafted Proxy header in an HTTP request, as demonstrated by (1) an application that makes a getenv('HTTP_PROXY') call or (2) a CGI configuration of PHP, aka an "httpoxy" issue.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 02/02/2023
The CVE-2016-5385 vulnerability represents a critical security flaw in PHP versions through 7.0.8 that stems from inadequate handling of HTTP proxy environment variables. This issue directly violates RFC 3875 section 4.1.18 standards which establish proper namespace conventions for HTTP headers and environment variables. The vulnerability arises because PHP fails to properly sanitize or validate the HTTP_PROXY environment variable that can be manipulated by malicious actors through crafted HTTP Proxy headers in incoming requests. When PHP applications process these requests, they may inadvertently use untrusted client data from the HTTP_PROXY variable, creating a pathway for attackers to redirect outbound HTTP traffic through arbitrary proxy servers.
The technical exploitation of this vulnerability occurs through HTTP request manipulation where attackers craft malicious Proxy headers that get processed by PHP applications. When PHP processes these headers, it may populate the HTTP_PROXY environment variable with attacker-controlled data without proper validation. This creates a situation where applications that rely on getenv('HTTP_PROXY') calls or those running in CGI configurations become vulnerable to man-in-the-middle attacks. The flaw is particularly dangerous because it allows attackers to intercept or redirect network traffic from PHP applications to malicious proxy servers, potentially enabling data exfiltration, traffic manipulation, or further attack vectors.
The operational impact of CVE-2016-5385 extends beyond simple traffic redirection as it fundamentally compromises application security posture. Applications using PHP versions affected by this vulnerability face risks including unauthorized data access, traffic interception, and potential compromise of sensitive communications. The vulnerability affects both standard PHP installations and CGI configurations, making it particularly widespread in web server environments. Security researchers have classified this issue under the broader category of insecure input handling and environment variable manipulation, which aligns with CWE-20 (Improper Input Validation) and CWE-118 (Improper Access Control). This vulnerability also maps to ATT&CK technique T1071.004 (Application Layer Protocol: DNS) and T1041 (Exfiltration Over C2 Channel) when exploited in conjunction with other attack vectors.
Mitigation strategies for CVE-2016-5385 focus on both immediate patching and operational hardening measures. The primary solution involves upgrading to PHP versions 7.0.9 or later where this vulnerability has been addressed through proper environment variable sanitization. Organizations should also implement strict input validation for HTTP headers and environment variables, particularly in CGI environments where the vulnerability is most pronounced. Additional protective measures include configuring web servers to strip or sanitize Proxy headers before they reach PHP applications, implementing network-level controls to restrict outbound proxy traffic, and monitoring for unusual proxy server connections. Security teams should conduct comprehensive vulnerability assessments across all PHP applications to identify those potentially affected by this issue, particularly focusing on applications that make getenv() calls for HTTP_PROXY variables. The remediation process should also include reviewing application code for proper environment variable handling and implementing security controls that prevent untrusted data from influencing proxy configuration parameters.