CVE-2026-87939 in Feed Block Plugin
Summary
by MITRE • 10/22/2026
Improper Neutralization of Input During Web Page Generation ("Cross-site Scripting") vulnerability in Drupal Feed Block allows Stored XSS. This issue affects Feed Block versions: from 0.0.0 to 2.0.2, from 3.0.0 to 3.0.2.
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Analysis
by VulDB Data Team • 10/22/2026
The identified security flaw represents a classic instance of Improper Neutralization of Input During Web Page Generation, commonly known as Cross-Site Scripting or XSS. Specifically, this vulnerability is located within the Drupal Feed Block module and manifests as a Stored XSS issue. This classification indicates that malicious script payloads are not merely executed in transient contexts but are persistently stored on the target server's database or file system. When other users subsequently access pages containing these feeds, the injected scripts execute automatically within their browser sessions, leading to persistent compromise of user data and session integrity. The vulnerability affects a broad range of versions for this module, specifically impacting releases from version 0.0.0 through 2.0.2 as well as versions 3.0.0 through 3.0.2. This wide span suggests that the underlying input validation logic was either fundamentally flawed or inconsistently applied across multiple major and minor iterations of the software.
From a technical perspective, the root cause lies in the module's failure to properly sanitize user-supplied data before it is rendered into HTML output within web pages generated by Drupal. In typical Feed Block operations, content from external RSS or Atom feeds may be processed and displayed on the site. If the application fails to escape special characters such as angle brackets, quotes, and ampersands, an attacker can inject executable JavaScript code directly into these feed items. Because this is a stored vulnerability, the malicious payload remains active until it is manually removed from the database or the offending content is deleted. This persistence distinguishes it from reflected XSS attacks, where the payload exists only in the URL query string and requires user interaction to trigger execution each time. The lack of robust output encoding allows the browser's parser to interpret the injected strings as executable code rather than plain text data.
The operational impact of this vulnerability is severe due to its persistent nature. Attackers can exploit Stored XSS to steal sensitive information such as session cookies, authentication tokens, and personally identifiable information stored in local storage or form fields. By hijacking user sessions, an attacker may gain unauthorized access to administrative accounts if the victim has elevated privileges, potentially leading to full site compromise. Furthermore, attackers can use this vector to perform actions on behalf of the victim without their knowledge, such as changing account settings, posting malicious content, or defacing the website's public-facing pages. The ability to execute arbitrary JavaScript also enables phishing attacks where fake login forms are injected into legitimate pages, tricking users into surrendering credentials. Given that Drupal is a widely used CMS, the potential blast radius of this vulnerability extends across numerous organizations relying on affected versions for their content management infrastructure.
In terms of industry standard classifications, this flaw aligns with CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'). The specific mechanism of storing malicious scripts in a database and executing them later corresponds to the Stored XSS sub-category within this weakness definition. From an offensive security perspective, such as the MITRE ATT&CK framework, this vulnerability facilitates techniques related to Client-side Injection (T1059) and potentially Credential Access via Browser Session Hijacking if session tokens are exfiltrated. The persistence of the attack vector means that remediation is not merely about patching a single entry point but requires addressing systemic input handling practices within the module's codebase.
Mitigation strategies must prioritize immediate upgrading to patched versions of the Feed Block module where these issues have been resolved by the developers. Administrators should verify their current version against the affected ranges and apply updates as soon as they become available from official Drupal channels. In cases where patching is not immediately feasible, temporary mitigations may include implementing strict Content Security Policy headers that restrict script execution to trusted sources only, thereby preventing inline scripts injected via XSS from executing even if successfully stored in the database. Additionally, input validation should be enforced at multiple layers, ensuring that all data entering the system is sanitized against a whitelist of allowed characters rather than relying solely on blacklist approaches which are prone to bypasses. Regular security audits and code reviews focusing on output encoding practices can further reduce the risk of similar vulnerabilities arising in other parts of the application ecosystem.