CVE-2017-7272 in PHP
Summary
by MITRE
PHP through 7.1.3 enables potential SSRF in applications that accept an fsockopen hostname argument with an expectation that the port number is constrained. Because a :port syntax is recognized, fsockopen will use the port number that is specified in the hostname argument, instead of the port number in the second argument of the function.
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Analysis
by VulDB Data Team • 11/22/2022
The vulnerability described in CVE-2017-7272 represents a significant server-side request forgery issue within PHP versions through 7.1.3, specifically affecting applications that utilize the fsockopen function for network communications. This flaw stems from improper handling of hostname arguments that contain port specifications, creating a dangerous misalignment between expected and actual network behavior. The vulnerability operates at the application layer and can be exploited by malicious actors to bypass intended network restrictions and access internal systems that should otherwise be protected from external requests.
The technical root cause of this vulnerability lies in how PHP's fsockopen function processes hostname arguments containing colon-separated port specifications. When an application passes a hostname string that includes a port number in the format "hostname:port" to fsockopen, the function incorrectly prioritizes the port specified within the hostname over the explicit port parameter provided in the function call's second argument. This behavior creates a scenario where attackers can manipulate the target port by embedding it directly within the hostname string, effectively overriding the intended port constraints that applications typically enforce. The flaw operates under CWE-918, which specifically addresses server-side request forgery vulnerabilities where applications fail to properly validate or sanitize external input that influences network requests.
The operational impact of this vulnerability extends beyond simple network access bypass, as it can enable attackers to perform unauthorized connections to internal services that are not meant to be accessible from external networks. Applications that rely on fsockopen for connecting to external services or databases may inadvertently allow attackers to redirect these connections to internal systems such as databases, administrative interfaces, or other sensitive services running on different ports. This creates a pathway for attackers to potentially escalate their privileges, access sensitive data, or perform further reconnaissance within the network environment. The vulnerability is particularly dangerous in environments where applications are configured to connect to specific external endpoints but lack proper input validation for the hostname parameter.
Security practitioners should implement multiple layers of mitigation to address this vulnerability effectively. The most direct approach involves updating affected PHP installations to versions that resolve this behavior, as newer releases properly handle the port specification precedence. Additionally, applications should validate and sanitize all hostname inputs passed to fsockopen functions, ensuring that port specifications within hostname strings are either stripped or validated against acceptable ranges. Input validation strategies should include regular expression checks to prevent colon-separated port specifications in hostname parameters, while also implementing proper network segmentation and firewall rules to limit access to internal services. Organizations should also consider implementing network monitoring to detect unusual outbound connection patterns that might indicate exploitation attempts. The vulnerability's characteristics align with ATT&CK technique T1071.004, which covers application layer protocol manipulation, and represents a classic example of how improper input handling can create security weaknesses that enable broader attack vectors.