{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata — refreshed continuously.","feed_url":"https://feed.craftedsignal.io/tags/mistune/","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cves":[],"_cs_exploited":false,"_cs_products":["mistune (= 3.2.0)"],"_cs_severities":["medium"],"_cs_tags":["dos","vulnerability","mistune"],"_cs_type":"advisory","_cs_vendors":["pip"],"content_html":"\u003cp\u003eA denial-of-service vulnerability has been identified in Mistune version 3.2.0, a Python Markdown parser. This vulnerability stems from the \u003ccode\u003eparse_link_title()\u003c/code\u003e function within \u003ccode\u003ehelpers.py\u003c/code\u003e, which is susceptible to excessive backtracking and parsing loops when processing malformed reference links. An attacker can exploit this by providing specially crafted Markdown input that causes the application to consume excessive CPU resources, leading to application hangs and service unavailability. Publicly available PoC exploit code demonstrates the vulnerability. This poses a significant threat to applications that rely on Mistune to parse untrusted Markdown content, such as web applications and APIs.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAn attacker crafts a malicious Markdown document containing specially crafted reference links with excessive escape character sequences.\u003c/li\u003e\n\u003cli\u003eThe attacker submits the malicious Markdown document to a web application or API that uses Mistune for Markdown parsing.\u003c/li\u003e\n\u003cli\u003eThe application calls the \u003ccode\u003emistune.html()\u003c/code\u003e function to render the Markdown content into HTML.\u003c/li\u003e\n\u003cli\u003eWithin \u003ccode\u003emistune.html()\u003c/code\u003e, the \u003ccode\u003eparse\u003c/code\u003e method in \u003ccode\u003emistune/markdown.py\u003c/code\u003e is invoked.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003eparse_ref_link\u003c/code\u003e function in \u003ccode\u003emistune/block_parser.py\u003c/code\u003e is called to process the reference links.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003eparse_link_title\u003c/code\u003e function in \u003ccode\u003emistune/helpers.py\u003c/code\u003e is then called to parse the link title.\u003c/li\u003e\n\u003cli\u003eDue to the malformed reference link structure, \u003ccode\u003eparse_link_title\u003c/code\u003e enters an excessive parsing loop with significant backtracking.\u003c/li\u003e\n\u003cli\u003eThe excessive parsing consumes CPU resources, eventually leading to a denial-of-service condition as the application hangs and becomes unresponsive.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation of this vulnerability results in a denial-of-service (DoS) condition. Specifically, the targeted application experiences high CPU usage and ultimately hangs, rendering it unavailable to legitimate users. This can disrupt services, cause financial losses, and damage the reputation of organizations that rely on the affected application. The vulnerability impacts any application using Mistune 3.2.0 to parse untrusted markdown, including web applications and APIs.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eApply mitigations suggested by the vendor, including parsing depth and iteration limits within \u003ccode\u003eparse_link_title()\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003eImplement input validation to limit reference-link title length, mitigating the impact of excessively long titles.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u003ccode\u003eMistune_DOS_Process_CPU_Spike\u003c/code\u003e to detect processes exhibiting high CPU usage during Markdown parsing.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u003ccode\u003eMistune_DOS_Request_Pattern\u003c/code\u003e to detect suspicious request patterns indicative of the exploit being attempted.\u003c/li\u003e\n\u003cli\u003eMonitor web server logs for suspicious requests containing excessive escape character sequences indicative of the provided PoC exploit.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-05-06T16:56:26Z","date_published":"2026-05-06T16:56:26Z","id":"/briefs/2026-05-mistune-dos/","summary":"A denial-of-service vulnerability exists in Mistune version 3.2.0 due to excessive parsing and CPU consumption when processing specially crafted reference links, leading to application hangs and service unavailability.","title":"Mistune Markdown Parser Denial-of-Service Vulnerability","url":"https://feed.craftedsignal.io/briefs/2026-05-mistune-dos/"}],"language":"en","title":"CraftedSignal Threat Feed — Mistune","version":"https://jsonfeed.org/version/1.1"}