CVE-2021-3767 in BookStack
Summary
by MITRE • 09/06/2021
bookstack is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
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Analysis
by VulDB Data Team • 09/09/2021
The vulnerability identified as CVE-2021-3767 affects BookStack, a wiki platform that allows users to create and manage documentation through web-based interfaces. This particular weakness manifests as an improper neutralization of input during web page generation, creating a cross-site scripting vulnerability that can be exploited by malicious actors to inject and execute arbitrary script code within the context of a victim's browser session. The flaw resides in how the application processes user-supplied content when rendering web pages, failing to adequately sanitize or escape potentially dangerous input before incorporating it into dynamic HTML output.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding mechanisms within BookStack's content rendering pipeline. When users create or edit pages, the system accepts various input formats including markdown and HTML content without proper sanitization of script tags, event handlers, or other malicious code patterns. Attackers can craft malicious payloads that, when rendered by the application, execute within the browser context of authenticated users, potentially leading to session hijacking, privilege escalation, or data exfiltration. This weakness directly maps to CWE-79, which defines Cross-Site Scripting as a condition where untrusted data is incorporated into web pages without proper validation or escaping, allowing attackers to inject client-side scripts.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable sophisticated attack chains that leverage the victim's authenticated session. An attacker who successfully exploits this vulnerability could gain access to sensitive information, modify content, delete pages, or even escalate privileges if the affected user possesses administrative capabilities. The vulnerability affects both authenticated and unauthenticated users depending on the specific implementation details, making it particularly dangerous in environments where users have varying permission levels. The attack surface includes any functionality that accepts user input for display in web pages, such as page titles, content fields, comments, and search queries, all of which could serve as potential entry points for malicious script injection.
Mitigation strategies for this vulnerability should focus on implementing comprehensive input sanitization and output encoding mechanisms throughout the application's data flow. Organizations should deploy proper content security policies that restrict script execution and implement strict input validation that filters out or escapes dangerous characters and patterns. The application should employ context-aware output encoding that ensures user-supplied content is properly escaped based on the target context where it will be rendered. Additionally, implementing web application firewalls with XSS detection capabilities and regular security testing can provide additional layers of protection. Security updates should be applied immediately upon availability, and administrators should conduct thorough input validation testing to ensure all user-facing interfaces properly handle potentially malicious input. This vulnerability aligns with ATT&CK technique T1059.007, which describes the use of script-based commands and techniques to execute malicious code within compromised environments, emphasizing the need for robust input sanitization as a primary defensive measure.