CVE-2018-19289 in Valine
Summary
by MITRE
An issue was discovered in Valine v1.3.3. It allows HTML injection, which can be exploited for JavaScript execution via an EMBED element in conjunction with a .pdf file.
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Analysis
by VulDB Data Team • 06/06/2023
The vulnerability identified as CVE-2018-19289 represents a critical HTML injection flaw within the Valine commenting system version 1.3.3. This issue stems from insufficient input validation and sanitization mechanisms that fail to properly filter user-supplied content before rendering it within the application's output. The vulnerability specifically manifests when the system processes embedded content through EMBED elements, creating a pathway for malicious actors to inject arbitrary HTML and JavaScript code into the application's display layer.
The technical exploitation of this vulnerability leverages the EMBED element's ability to load external resources, particularly PDF files, which can contain malicious payloads that trigger JavaScript execution when rendered in the browser context. This type of vulnerability falls under CWE-79 - Improper Neutralization of Input During Web Page Generation, which specifically addresses the failure to properly sanitize user input before incorporating it into web content. The flaw demonstrates a classic cross-site scripting vulnerability where attacker-controlled data flows directly into the HTML output without proper encoding or sanitization.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the ability to perform session hijacking, defacement of content, data exfiltration, and potential privilege escalation within the application's context. When users view comments containing malicious EMBED elements referencing crafted PDF files, the JavaScript code embedded within these resources executes in the context of the victim's browser session. This creates a persistent threat vector that can be exploited against any user who views affected content, making it particularly dangerous for comment systems where user-generated content is displayed to multiple visitors.
The exploitation chain typically involves an attacker crafting a comment containing an EMBED tag that references a malicious PDF file hosted on a server controlled by the attacker. The PDF file contains embedded JavaScript that executes upon rendering, potentially stealing cookies, redirecting users to malicious sites, or performing other malicious actions. This vulnerability aligns with ATT&CK technique T1211 - Exploitation for Defense Evasion, as the malicious code execution can bypass security controls by leveraging legitimate application functionality. Additionally, it maps to T1059 - Command and Scripting Interpreter, where JavaScript is used as the execution vehicle.
Mitigation strategies for this vulnerability should include comprehensive input sanitization and validation of all user-supplied content, particularly around HTML elements and embedded resources. Implementing a strict Content Security Policy (CSP) that restricts the execution of inline scripts and limits the sources from which embedded content can be loaded provides an additional layer of protection. The application should sanitize all user input by removing or encoding potentially dangerous HTML elements and attributes, particularly EMBED, OBJECT, and SCRIPT tags. Regular updates and patches to the Valine commenting system should be implemented immediately upon release of security fixes, and organizations should consider implementing web application firewalls to detect and block suspicious patterns in user submissions. The vulnerability underscores the importance of proper input validation and output encoding as fundamental security practices in web application development, aligning with OWASP Top Ten security controls for preventing injection attacks.