CVE-2020-26298 in Redcarpet
Summary
by MITRE • 01/12/2021
Redcarpet is a Ruby library for Markdown processing. In Redcarpet before version 3.5.1, there is an injection vulnerability which can enable a cross-site scripting attack. In affected versions no HTML escaping was being performed when processing quotes. This applies even when the `:escape_html` option was being used. This is fixed in version 3.5.1 by the referenced commit.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 02/11/2021
The vulnerability identified as CVE-2020-26298 affects the Redcarpet Ruby library, a widely-used Markdown processing component that converts Markdown text into HTML format. This library serves as a critical dependency for numerous web applications and content management systems that rely on Markdown for document formatting and rendering. The flaw represents a significant security weakness that directly impacts the integrity and safety of web applications using this library, potentially allowing malicious actors to inject harmful content through carefully crafted Markdown input.
The technical nature of this vulnerability stems from inadequate HTML escaping mechanisms within the Redcarpet library's quote processing functionality. Specifically, when the library processes Markdown content containing quotes, it fails to properly escape HTML characters, even when the `:escape_html` option is explicitly enabled by developers. This oversight creates a pathway for cross-site scripting attacks where malicious input can bypass intended security measures and execute arbitrary JavaScript code in the context of users' browsers. The vulnerability manifests because the library's HTML escaping logic is not consistently applied across all processing paths, particularly in quote handling scenarios.
The operational impact of this vulnerability extends beyond simple XSS attacks, as it can enable attackers to compromise user sessions, steal sensitive information, manipulate web application functionality, and potentially escalate privileges within affected systems. When applications using Redcarpet process untrusted Markdown input from users, malicious actors can craft input that includes HTML tags and JavaScript code that gets rendered as part of the final HTML output. The vulnerability is particularly dangerous because it persists even when developers attempt to protect against XSS by enabling the HTML escaping option, creating a false sense of security that can lead to catastrophic consequences in production environments.
Security professionals should note that this vulnerability aligns with CWE-79, which specifically addresses cross-site scripting flaws in web applications, and demonstrates how improper input validation and output encoding can create exploitable conditions. The ATT&CK framework categorizes this as a code injection technique that can be leveraged for initial access and privilege escalation within web application environments. Organizations using Redcarpet in their applications must urgently upgrade to version 3.5.1 or later, as this release includes the necessary commit that properly implements HTML escaping for quote processing. Additionally, system administrators should conduct comprehensive security audits to identify any applications that may be vulnerable and implement proper input sanitization measures as additional defense-in-depth strategies.