CVE-2017-7189 in PHP
Summary
by MITRE
main/streams/xp_socket.c in PHP 7.x before 2017-03-07 misparses fsockopen calls, such as by interpreting fsockopen('127.0.0.1:80', 443) as if the address/port were 127.0.0.1:80:443, which is later truncated to 127.0.0.1:80. This behavior has a security risk if the explicitly provided port number (i.e., 443 in this example) is hardcoded into an application as a security policy, but the hostname argument (i.e., 127.0.0.1:80 in this example) is obtained from untrusted input.
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Analysis
by VulDB Data Team • 10/24/2023
The vulnerability described in CVE-2017-7189 represents a critical input parsing flaw in PHP's socket handling mechanism that fundamentally undermines network security policies implemented through the fsockopen function. This issue resides within the main/streams/xp_socket.c file of PHP 7.x versions prior to the 2017-03-07 security patch, where the function fails to properly separate hostname and port components when processing socket connections. The flaw manifests when a developer provides a hostname argument containing an embedded port specification alongside an explicitly defined port parameter, creating a scenario where the parsing logic incorrectly interprets the combined information and subsequently truncates the connection string in an insecure manner.
The technical implementation of this vulnerability stems from improper string parsing logic that fails to distinguish between the port portion embedded within the hostname argument and the explicitly provided port parameter. When PHP processes a call such as fsockopen('127.0.0.1:80', 443), the system incorrectly treats the entire string '127.0.0.1:80' as a single hostname component and then attempts to parse the port from this composite string. The subsequent truncation process strips away the intended port specification, effectively converting the connection attempt to use the embedded port (80) rather than the explicitly requested port (443). This behavior creates a significant security risk when applications implement security policies that rely on explicit port specifications to enforce network isolation or access controls.
From an operational security perspective, this vulnerability directly enables attackers to bypass network security controls that depend on explicit port specifications within application code. The flaw is particularly dangerous when applications use hardcoded port numbers as security policy enforcement mechanisms, such as requiring connections to specific secure ports for sensitive operations. Attackers can exploit this by providing malicious hostname input that contains embedded port specifications, effectively forcing the application to connect to unintended ports while maintaining the appearance of legitimate network activity. This type of vulnerability falls under CWE-129 Input Validation and Output Encoding, specifically addressing improper input validation of network connection parameters.
The security implications extend beyond simple port bypassing to encompass potential privilege escalation and service manipulation attacks. When applications enforce security policies through explicit port specifications, such as requiring connections to SSL ports (443) or specific service ports, this vulnerability allows adversaries to circumvent these controls by manipulating the hostname argument. The flaw aligns with ATT&CK technique T1071.004 Application Layer Protocol: SSH, where attackers manipulate network protocols to gain unauthorized access, though in this case the manipulation occurs at the socket level rather than the protocol level. Organizations implementing security policies that rely on explicit port specifications for network segmentation or access control are particularly vulnerable to this type of attack.
Mitigation strategies for CVE-2017-7189 require immediate patching of affected PHP installations to version 7.x released after March 7, 2017, which contains the corrected parsing logic. Additionally, developers should implement proper input validation for all hostname arguments passed to socket functions, separating embedded port specifications from explicit port parameters before processing. Security-conscious applications should validate that the final resolved connection parameters match expected security policies, particularly when dealing with user-supplied input. Organizations should also consider implementing network monitoring to detect anomalous connection patterns that might indicate exploitation attempts, as the vulnerability can be used to establish connections to unintended network endpoints while maintaining the appearance of legitimate application behavior. The vulnerability demonstrates the critical importance of proper input validation in network security contexts and the potential for seemingly minor parsing flaws to create significant security risks.