CVE-2018-20148 in WordPress
Summary
by MITRE
In WordPress versions before 5.0.1, contributors could conduct PHP object injection attacks via crafted metadata.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 06/19/2023
WordPress versions prior to 5.0.1 contained a critical vulnerability in the metadata handling system that allowed contributors with minimal privileges to execute PHP object injection attacks through maliciously crafted metadata inputs. This vulnerability originated from insufficient input validation and sanitization within the WordPress core metadata processing functions, specifically affecting how the system handled serialized data during metadata storage and retrieval operations. The flaw was particularly dangerous because it leveraged the inherent trust WordPress places in metadata fields, allowing unauthorized users to inject malicious serialized objects that would be unserialized during normal system operations.
The technical implementation of this vulnerability stemmed from the lack of proper sanitization in the wp_insert_post function and related metadata handling routines. When contributors submitted posts containing specially crafted metadata values, the system would accept these inputs without adequate validation, leading to potential object injection during the unserialization process. This type of vulnerability falls under CWE-502, which specifically addresses deserialization of untrusted data, making it a prime target for attackers seeking to escalate privileges or execute arbitrary code on vulnerable systems. The attack vector was particularly insidious because it required no elevated privileges beyond contributor level, making it accessible to users who normally had limited capabilities within the WordPress ecosystem.
The operational impact of this vulnerability was significant across multiple threat scenarios including privilege escalation, remote code execution, and potential data compromise. Attackers could exploit this flaw to elevate their privileges from contributor to administrator level, potentially gaining full control over WordPress installations. The vulnerability also enabled attackers to execute arbitrary PHP code on affected systems, leading to potential data theft, website defacement, or server compromise. This issue particularly affected WordPress installations where contributors had access to the admin panel, as the metadata injection could be performed through standard post submission processes without requiring additional authentication or specialized tools.
Mitigation strategies for CVE-2018-20148 focused primarily on immediate system updates to WordPress 5.0.1 or later versions where the vulnerability was patched through enhanced input validation and sanitization routines. Organizations should have implemented comprehensive monitoring of metadata fields and user activity logs to detect suspicious submissions. The patch introduced stricter validation of serialized data within WordPress metadata handling, ensuring that any potentially malicious objects would be rejected before processing. Additionally, implementing network-level protections such as web application firewalls and restricting contributor access to metadata fields could have provided additional defense in depth. This vulnerability aligns with ATT&CK technique T1059.007 for PHP and T1499.004 for unauthorized modification of web applications, demonstrating how seemingly minor input validation flaws can create substantial security risks in content management systems.