CVE-2026-1854 in Post Flagger Plugin
Summary
by MITRE • 03/21/2026
The Post Flagger plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'flag' shortcode in all versions up to, and including, 1.1 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
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Analysis
by VulDB Data Team • 03/21/2026
The Post Flagger plugin for WordPress presents a critical stored cross-site scripting vulnerability identified as CVE-2026-1854, affecting all versions through 1.1. This vulnerability stems from inadequate input sanitization and output escaping mechanisms within the plugin's 'flag' shortcode implementation, creating a persistent security weakness that can be exploited by authenticated attackers. The flaw specifically targets the plugin's handling of user-supplied attributes, allowing malicious actors to inject malicious scripts that persist in the application's database and execute whenever affected pages are accessed.
The technical exploitation of this vulnerability occurs through the improper handling of user input within the shortcode attribute processing. When an authenticated user with contributor-level privileges or higher submits content containing malicious script code through the flag shortcode parameters, the plugin fails to adequately sanitize these inputs before storing them. This insufficient sanitization combined with inadequate output escaping creates a persistent XSS vector where malicious scripts are stored in the database and executed in the context of other users' browsers when they access pages containing the injected content. The vulnerability operates at the application layer and specifically targets the WordPress content management system's shortcode processing mechanism.
The operational impact of CVE-2026-1854 extends beyond simple script execution, as it enables authenticated attackers to leverage the compromised plugin for more sophisticated attacks. An attacker with contributor privileges can inject scripts that may steal session cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users. The stored nature of the vulnerability means that once injected, the malicious code persists until manually removed from the database, potentially affecting all users who access pages containing the compromised shortcode. This makes the vulnerability particularly dangerous in environments where multiple contributors have access to the WordPress installation, as it provides a persistent backdoor for attackers to maintain access and execute malicious activities.
Mitigation strategies for this vulnerability require immediate action including updating to the patched version of the Post Flagger plugin, implementing proper input validation and output escaping mechanisms, and conducting thorough security reviews of all plugin components. Organizations should also consider implementing web application firewalls to detect and block suspicious script injection attempts, while establishing regular security audits of WordPress plugins to identify similar vulnerabilities. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws, and represents a clear violation of the principle of least privilege as it allows users with relatively low access levels to execute arbitrary code within the application context. Additionally, this vulnerability maps to ATT&CK technique T1566 which covers social engineering through malicious content injection, making it a significant concern for organizations implementing WordPress-based content management solutions.