CVE-2017-16006 in remarkable
Summary
by MITRE
Remarkable is a markdown parser. In versions 1.6.2 and lower, remarkable allows the use of `data:` URIs in links and can therefore execute javascript.
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Analysis
by VulDB Data Team • 03/21/2023
The CVE-2017-16006 vulnerability affects Remarkable, a popular markdown parser library, by permitting the execution of arbitrary javascript code through the use of data URIs in hyperlinks. This represents a critical security flaw that undermines the fundamental security assumptions of markdown processing applications. The vulnerability stems from insufficient input validation and sanitization within the parser's handling of hyperlink attributes, specifically failing to properly filter or reject potentially dangerous data URI schemes that can contain executable javascript code.
The technical flaw manifests when Remarkable processes markdown content containing links with data URIs that begin with the data: scheme. These URIs can contain javascript code that gets executed when the parsed HTML is rendered in a web browser context. The vulnerability exists because the parser does not adequately distinguish between safe and unsafe URI schemes, allowing malicious actors to embed javascript payloads directly within markdown documents. This type of vulnerability falls under CWE-20, which describes improper input validation, and specifically relates to CWE-79, which covers cross-site scripting attacks through improper sanitization of input data. The flaw enables attackers to construct malicious markdown documents that, when processed by vulnerable versions of Remarkable, can execute arbitrary javascript code in the context of the user's browser session.
The operational impact of this vulnerability is severe and far-reaching, particularly for applications that process untrusted markdown content from users or external sources. Any system using Remarkable version 1.6.2 or earlier to render user-generated markdown content becomes vulnerable to cross-site scripting attacks that can lead to session hijacking, data exfiltration, and other malicious activities. The vulnerability is particularly dangerous in web applications, content management systems, or collaborative platforms where users can submit markdown content that gets rendered for other users. Attackers can craft malicious markdown documents containing links with data: URIs that execute javascript code, potentially stealing cookies, redirecting users to phishing sites, or performing actions on behalf of authenticated users. This vulnerability directly maps to ATT&CK technique T1203, which describes exploitation of web applications through cross-site scripting, and T1059, covering the execution of malicious code through scripting languages.
The recommended mitigations for CVE-2017-16006 involve immediate upgrading to Remarkable version 1.6.3 or later, which contains the necessary fixes to properly sanitize and validate URI schemes in hyperlink attributes. Organizations should implement comprehensive input validation measures that explicitly reject or sanitize data URIs and other potentially dangerous URI schemes before processing markdown content. Additional protective measures include implementing content security policies that restrict the execution of inline javascript, using a secure markdown rendering library that properly handles URI validation, and conducting regular security audits of all markdown processing components within the application stack. Security teams should also consider implementing web application firewalls that can detect and block suspicious data URI patterns in incoming requests. The vulnerability highlights the importance of proper URI sanitization in web applications and serves as a reminder that even seemingly benign parsing libraries can become attack vectors when they fail to properly validate input data against known dangerous patterns.