CVE-2020-18221 in Typora
Summary
by MITRE • 05/26/2021
Cross Site Scripting (XSS) in Typora v0.9.65 and earlier allows remote attackers to execute arbitrary code by injecting commands during block rendering of a mathematical formula.
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Analysis
by VulDB Data Team • 05/29/2021
This vulnerability represents a critical cross site scripting flaw in Typora version 0.9.65 and earlier, where remote attackers can inject malicious code through mathematical formula block rendering. The vulnerability stems from insufficient input validation and sanitization during the processing of mathematical expressions, allowing attackers to execute arbitrary code on affected systems. The flaw specifically manifests when the application processes mathematical formulas within document blocks, creating an execution path that bypasses normal security controls.
The technical implementation of this vulnerability leverages the application's handling of mathematical notation within its markdown processing engine. When users create mathematical formulas using LaTeX syntax or similar markup, the application renders these elements in a way that fails to properly escape or sanitize user input. This creates a classic XSS vector where attacker-controlled content can be executed in the context of the victim's browser session. The vulnerability operates at the intersection of web application security and document processing systems, where mathematical rendering components become attack surfaces.
The operational impact of this vulnerability extends beyond simple code execution, as it enables attackers to perform session hijacking, data theft, and persistence mechanisms within affected environments. An attacker could craft malicious mathematical formulas that, when rendered by the vulnerable Typora application, would execute malicious JavaScript code in the context of the user's browser. This capability allows for comprehensive attack chains including credential theft, redirection to malicious sites, and potential privilege escalation within the application's execution context. The vulnerability affects both local and remote execution scenarios where the application processes user-generated content.
Mitigation strategies for this vulnerability should focus on immediate patching of the Typora application to version 0.9.66 or later, which contains the necessary input validation and sanitization fixes. Additionally, organizations should implement strict content filtering policies that prevent the execution of potentially malicious code within document processing environments. Security controls should include input validation at multiple layers, including client-side sanitization of mathematical expressions and server-side validation of all user-generated content. This vulnerability aligns with CWE-79, which specifically addresses cross site scripting flaws, and maps to ATT&CK technique T1203, which covers exploitation of web applications through XSS vulnerabilities. The remediation approach should incorporate defense in depth principles, ensuring that multiple security controls work together to prevent similar vulnerabilities from being exploited in other components of the application stack.