CVE-2015-9503 in Modern Theme
Summary
by MITRE
The Modern theme before 1.4.2 for WordPress has XSS via the genericons/example.html anchor identifier.
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Analysis
by VulDB Data Team • 01/17/2024
The vulnerability identified as CVE-2015-9503 affects the Modern theme for WordPress prior to version 1.4.2, specifically targeting cross-site scripting flaws within the genericons/example.html file. This issue arises from improper input validation and sanitization mechanisms that fail to adequately filter user-supplied data before rendering it in web pages. The vulnerability exists in the theme's handling of anchor identifiers within the example.html file, which serves as a demonstration of the genericons library functionality. When malicious users craft specially formatted anchor identifiers containing script tags or other malicious code, the theme fails to properly escape or sanitize these inputs, creating an avenue for attackers to inject arbitrary JavaScript code into web pages viewed by other users.
The technical flaw stems from the theme's insecure direct object reference vulnerability, which allows unauthorized access to internal resources through manipulation of input parameters. This weakness enables attackers to inject malicious payloads through the anchor identifier parameter in the genericons/example.html endpoint. The vulnerability can be classified under CWE-79 as Cross-Site Scripting, specifically targeting the scenario where user-controllable data is directly included in web page content without proper sanitization. The Modern theme's implementation fails to properly validate and sanitize the anchor identifier parameter, allowing malicious scripts to execute in the context of other users' browsers, potentially leading to session hijacking, data theft, or further exploitation of the compromised systems.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to perform session hijacking attacks, steal cookies, redirect users to malicious sites, or even execute more sophisticated attacks such as credential harvesting. When exploited, this vulnerability allows attackers to compromise the integrity of the WordPress site and potentially gain unauthorized access to user accounts. The vulnerability affects all users of the affected theme versions, creating a widespread security risk for WordPress installations that utilize the Modern theme. The attack vector is particularly concerning because it requires minimal user interaction beyond visiting the vulnerable page, making it an attractive target for automated exploitation campaigns. This vulnerability also potentially enables privilege escalation attacks when combined with other weaknesses in the WordPress ecosystem.
Mitigation strategies for CVE-2015-9503 should prioritize immediate patching of the affected theme to version 1.4.2 or later, which includes proper input sanitization and validation mechanisms. Organizations should implement comprehensive input validation for all user-supplied data, particularly within theme files and plugin components that handle external inputs. The implementation of Content Security Policy headers can provide additional protection against script execution, while proper output encoding and escaping techniques should be enforced throughout the theme's codebase. Security monitoring should be enhanced to detect unusual access patterns to theme files, and regular security audits of WordPress themes and plugins should be conducted to identify similar vulnerabilities. The ATT&CK framework categorizes this vulnerability under T1059.007 for scripting and T1566 for phishing, highlighting the need for layered defensive measures including user education, network monitoring, and proper security configuration practices to prevent exploitation.