{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/vendors/mistune-project/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":["cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*"],"_cs_cves":[{"cvss":4.3,"id":"CVE-2026-59930"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Mistune"],"_cs_severities":["medium"],"_cs_tags":["vulnerability","markdown","client-side","cve"],"_cs_type":"advisory","_cs_vendors":["Mistune Project"],"content_html":"\u003cp\u003eA vulnerability, identified as CVE-2026-59930, has been disclosed in the Mistune markdown parser, specifically affecting its TableOfContents (toc) directive. This flaw stems from the parser's method of generating HTML heading IDs, which uses a predictable \u003ccode\u003etoc_N\u003c/code\u003e numbering scheme without proper slugification. This lack of uniqueness allows an attacker to craft malicious markdown content that includes pre-defined \u003ccode\u003eid=\u0026quot;toc_N\u0026quot;\u003c/code\u003e attributes. When rendered by an application using the vulnerable Mistune library, these attacker-controlled IDs can collide with the legitimate IDs generated for the table of contents. Such a collision could enable client-side content manipulation, link hijacking, or other adverse effects, potentially redirecting user interactions to attacker-controlled elements. The vulnerability highlights the importance of robust ID generation in web content rendering to prevent client-side interference.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAttacker identifies a web application or platform that uses the vulnerable Mistune markdown parser.\u003c/li\u003e\n\u003cli\u003eAttacker crafts malicious markdown content containing a legitimate TableOfContents directive.\u003c/li\u003e\n\u003cli\u003eWithin the same malicious markdown, the attacker embeds custom HTML content with an \u003ccode\u003eid\u003c/code\u003e attribute set to a predictable \u003ccode\u003etoc_N\u003c/code\u003e value, anticipating the IDs generated by the Mistune parser.\u003c/li\u003e\n\u003cli\u003eThe crafted markdown content is submitted to the vulnerable application, for example, through user input, forum posts, or content management systems.\u003c/li\u003e\n\u003cli\u003eThe application renders the malicious markdown using the vulnerable Mistune parser, which generates HTML output.\u003c/li\u003e\n\u003cli\u003eDue to the flaw in Mistune, the attacker's pre-defined \u003ccode\u003eid=\u0026quot;toc_N\u0026quot;\u003c/code\u003e collides with the ID generated by the legitimate TableOfContents.\u003c/li\u003e\n\u003cli\u003eWhen a user interacts with a legitimate TableOfContents link or a client-side script targets a specific \u003ccode\u003etoc_N\u003c/code\u003e ID, the browser's DOM resolution prioritizes the attacker-controlled element.\u003c/li\u003e\n\u003cli\u003eThis results in client-side content manipulation, redirection to attacker-controlled sections, or potential execution of embedded malicious scripts if combined with other client-side vulnerabilities.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eThe successful exploitation of CVE-2026-59930 could lead to various client-side impacts. Attackers could manipulate the content displayed to users by hijacking links within a Table of Contents, causing users to interact with unintended elements or sections of a webpage. This could facilitate phishing attempts, defacement of rendered markdown content, or user confusion. While not directly leading to server-side compromise, this vulnerability can undermine the integrity of information presented to users and serves as a potential vector for further client-side attacks if combined with XSS or similar flaws.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003ePrioritize updating the Mistune markdown parser to a version that addresses CVE-2026-59930.\u003c/li\u003e\n\u003cli\u003eImplement robust client-side input validation and sanitization for any user-submitted markdown content, specifically focusing on filtering or encoding HTML attributes and IDs.\u003c/li\u003e\n\u003cli\u003eReview web application configurations to ensure that client-side scripts do not rely solely on predictable or short HTML IDs for critical interactions, especially when rendering user-supplied content.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-07-11T07:35:28Z","date_published":"2026-07-11T07:35:28Z","id":"https://feed.craftedsignal.io/briefs/2026-07-mistune-toc-collision/","summary":"A vulnerability, CVE-2026-59930, in the Mistune markdown parser's TableOfContents directive creates predictable HTML heading IDs, enabling an attacker to inject content with colliding IDs for client-side content manipulation.","title":"Mistune Markdown Parser Vulnerability CVE-2026-59930 Allows HTML ID Collision","url":"https://feed.craftedsignal.io/briefs/2026-07-mistune-toc-collision/"}],"language":"en","title":"CraftedSignal Threat Feed - Mistune Project","version":"https://jsonfeed.org/version/1.1"}