CVE-2019-17220 in Rocket.Chat
Summary
by MITRE
Rocket.Chat before 2.1.0 allows XSS via a URL on a ![title] line.
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Analysis
by VulDB Data Team • 01/01/2025
The vulnerability identified as CVE-2019-17220 represents a cross-site scripting weakness in Rocket.Chat versions prior to 2.1.0 that specifically affects the markdown rendering functionality. This flaw exists within the client-side processing of markdown formatted text, particularly when handling image references that include URLs. The vulnerability occurs when a malicious user crafts a specially formatted markdown string containing an image reference with a malicious URL in the title attribute, which then gets rendered without proper sanitization in the web interface.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within Rocket.Chat's markdown parser. When processing a line formatted as , the application fails to properly sanitize the title parameter before rendering it in the HTML context. This creates an opportunity for attackers to inject malicious JavaScript code or other harmful content that executes in the context of other users' browsers. The vulnerability is categorized under CWE-79 as a Cross-Site Scripting flaw, specifically manifesting as a stored XSS attack vector when the malicious content is persisted within the application's database and subsequently rendered to other users.
The operational impact of this vulnerability is significant as it allows attackers to compromise user sessions and potentially escalate privileges within the Rocket.Chat environment. An attacker could craft malicious markdown content that, when viewed by other users, would execute arbitrary JavaScript code in their browsers. This could lead to session hijacking, data exfiltration, or further exploitation of the application. The vulnerability is particularly dangerous because it leverages the common markdown syntax used for creating image references, making it difficult to distinguish between legitimate and malicious content. This weakness aligns with ATT&CK technique T1211 which involves the exploitation of vulnerabilities to execute arbitrary code.
The attack surface for this vulnerability extends to any user who can post messages containing markdown content within Rocket.Chat channels or direct messages. This includes users with various permission levels who can contribute to discussions, making the impact widespread across typical deployment scenarios. Organizations using Rocket.Chat without proper input sanitization measures are at risk of having their users' sessions compromised, potentially leading to unauthorized access to sensitive communications and data within the platform. The vulnerability demonstrates a critical gap in the application's security posture and highlights the importance of proper input validation and output encoding in web applications.
Mitigation strategies for this vulnerability include upgrading to Rocket.Chat version 2.1.0 or later where the issue has been addressed through proper sanitization of markdown input. Organizations should also implement additional security measures such as content security policy headers, regular input validation checks, and user education about the risks of viewing untrusted content. The fix typically involves implementing proper HTML escaping or sanitization of user-provided content before rendering it in the browser context, ensuring that any potentially malicious input cannot be executed as code. Additionally, organizations should consider implementing web application firewalls and monitoring for suspicious markdown content patterns to detect potential exploitation attempts.