CVE-2018-10101 in WordPress
Summary
by MITRE
Before WordPress 4.9.5, the URL validator assumed URLs with the hostname localhost were on the same host as the WordPress server.
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Analysis
by VulDB Data Team • 02/28/2023
This vulnerability in WordPress versions prior to 4.9.5 represents a significant security flaw in the application's URL validation mechanism that could enable unauthorized access to internal network resources. The issue stems from how the application processes and validates URLs that contain the hostname localhost, treating them as if they reference the same host as the WordPress server itself rather than properly validating their actual network location. This misclassification creates a dangerous assumption that allows attackers to potentially access internal resources that should remain protected from external exposure.
The technical implementation of this vulnerability resides in WordPress's URL validation logic where localhost is treated as a special case that bypasses normal host validation procedures. When a URL contains localhost as the hostname, the validation function incorrectly assumes that this URL points to the same server hosting the WordPress installation rather than properly checking if it represents a legitimate internal network resource. This behavior violates fundamental security principles of network isolation and privilege separation, as it allows for potential internal network reconnaissance and access to services that should be restricted to local access only.
The operational impact of this vulnerability extends beyond simple information disclosure, as it could enable attackers to perform unauthorized access to internal services running on the same host as the WordPress server. An attacker could craft malicious URLs containing localhost that, when processed by the vulnerable WordPress application, would be interpreted as local resources, potentially allowing access to internal databases, administrative interfaces, or other sensitive services that are normally protected by network segmentation. This vulnerability particularly affects environments where WordPress is deployed on servers that also host internal services, creating a potential attack surface that could be exploited for privilege escalation or lateral movement within the network infrastructure.
This vulnerability aligns with CWE-20, which addresses "Improper Input Validation" and represents a specific case of inadequate validation of network resources. The flaw demonstrates poor security practices in URL parsing and validation that could be exploited as part of broader attack patterns. From an ATT&CK perspective, this vulnerability could be leveraged as part of the reconnaissance phase to identify internal network resources, potentially supporting techniques such as network sniffing or internal network discovery. The vulnerability also relates to privilege escalation techniques where an attacker might attempt to access local resources that should normally be restricted, making it a potential vector for more sophisticated attacks. Organizations should implement immediate patching to address this issue and consider network segmentation policies to limit exposure of internal services to potentially compromised WordPress installations. The fix in WordPress 4.9.5 properly validates localhost URLs against the actual host configuration rather than assuming local access, thereby restoring proper network isolation boundaries.