CVE-2016-2222 in WordPress
Summary
by MITRE
The wp_http_validate_url function in wp-includes/http.php in WordPress before 4.4.2 allows remote attackers to conduct server-side request forgery (SSRF) attacks via a zero value in the first octet of an IPv4 address.
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Analysis
by VulDB Data Team • 08/21/2022
The wp_http_validate_url function in WordPress versions prior to 4.4.2 contained a critical server-side request forgery vulnerability that allowed remote attackers to bypass URL validation mechanisms and make unauthorized requests to internal network resources. This vulnerability specifically targeted the IPv4 address parsing logic within WordPress's HTTP handling subsystem, where the function failed to properly validate the first octet of IPv4 addresses during URL validation processes. The flaw enabled attackers to craft malicious URLs that would pass WordPress's validation checks while still being processed by the underlying HTTP client, creating a pathway for unauthorized network access.
The technical implementation of this vulnerability stemmed from insufficient input sanitization within the URL validation routine. When WordPress encountered a URL containing an IPv4 address with a zero value in the first octet, such as 0192.168.1.1 or 000.000.000.000, the wp_http_validate_url function would incorrectly accept these addresses as valid while the actual HTTP request processing would interpret them according to standard IPv4 parsing rules. This discrepancy between validation and execution created a window where attackers could force WordPress to make requests to internal services that should have been blocked by the validation layer. The vulnerability mapped to CWE-918, Server-Side Request Forgery, which specifically addresses the issue of attackers manipulating applications into making unintended requests to internal resources.
The operational impact of this vulnerability was significant for WordPress installations, as it could potentially allow attackers to access internal network services, databases, or other systems that were not directly exposed to the internet. Attackers could leverage this flaw to perform reconnaissance of internal network topology, access internal APIs, or even exploit other vulnerabilities in internal services that were not accessible from the public internet. The vulnerability was particularly dangerous because it required no special privileges or authentication to exploit, making it accessible to anyone who could submit content to a vulnerable WordPress site, including comment submissions or upload mechanisms. This made it a prime target for attackers seeking to establish persistent access or conduct further reconnaissance.
Mitigation strategies for this vulnerability required immediate patching of WordPress installations to version 4.4.2 or later, which contained the corrected URL validation logic. Organizations should also implement network-level restrictions to prevent internal services from being accessible to WordPress installations, particularly when WordPress is hosted on public-facing servers. Additional protections included implementing proper network segmentation, using firewalls to restrict outbound connections from WordPress servers, and deploying web application firewalls to monitor and block suspicious URL patterns. The vulnerability highlighted the importance of thorough input validation and the need for consistent security practices throughout application layers, as the flaw existed in the HTTP handling component that was critical for many WordPress functionalities. Security teams should also consider implementing monitoring solutions to detect unusual outbound network requests from WordPress installations, which could indicate exploitation attempts. The incident reinforced the principles outlined in the ATT&CK framework under the T1071.004 technique for application layer protocol tunneling, where attackers leverage application vulnerabilities to bypass network security controls.