CVE-2017-15612 in Mistune
Summary
by MITRE
mistune.py in Mistune 0.7.4 allows XSS via an unexpected newline (such as in java\nscript:) or a crafted email address, related to the escape and autolink functions.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2017-15612 affects the mistune.py markdown parser version 0.7.4, specifically targeting cross-site scripting exploits through improper handling of newline characters and email address formatting. This issue resides within the library's escape and autolink functions, which are responsible for sanitizing and processing markdown content that contains potential security threats. The flaw demonstrates a classic input validation weakness where the parser fails to properly sanitize user-supplied content that includes unexpected line breaks or specially crafted email addresses.
The technical exploitation occurs when the mistune parser encounters markdown content containing javascript: protocol followed by unexpected newlines or malformed email addresses that trigger the autolink function. When these elements are processed through the escape mechanism, the parser does not adequately sanitize the content, allowing malicious scripts to persist in the rendered output. This vulnerability specifically leverages the parser's inability to properly handle edge cases in how it processes markdown links and automatic link detection. The flaw is categorized under CWE-79 as a cross-site scripting vulnerability, where the application fails to sanitize user input before rendering it in the browser context.
The operational impact of this vulnerability extends beyond simple script injection, as it can enable attackers to execute arbitrary JavaScript code within the context of users who view the affected markdown content. This poses significant risks to web applications that rely on mistune for processing user-generated markdown content, particularly those that do not implement additional input sanitization layers. The vulnerability is particularly dangerous in environments where users can submit content that gets rendered in web browsers, as it allows for session hijacking, data theft, and other malicious activities. Attackers can craft payloads that exploit the newline handling to bypass existing security measures, making this a persistent threat in applications that do not properly validate markdown content.
Mitigation strategies for CVE-2017-15612 require immediate implementation of the official patch released by the mistune maintainers, which addresses the specific handling of escape and autolink functions. Organizations should also implement additional input validation layers that explicitly check for javascript: protocols and malformed email addresses before processing markdown content. The ATT&CK framework categorizes this vulnerability under T1203 - Exploitation for Client Execution, as it enables attackers to execute malicious code through client-side vulnerabilities. Security teams should consider implementing content security policies and additional sanitization routines that can detect and neutralize suspicious markdown patterns. Regular security audits of markdown processing libraries and their configurations are essential to prevent similar vulnerabilities from being exploited in other components of the application stack.