{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/products/mistune-block_parser/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":["cpe:2.3:a:mistune_project:mistune:*:*:*:*:*:*:*:*"],"_cs_cves":[{"cvss":7.5,"id":"CVE-2026-59928"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["Mistune block_parser"],"_cs_severities":["medium"],"_cs_tags":["denial-of-service","vulnerability","markdown-parser"],"_cs_type":"advisory","_cs_vendors":["Mistune"],"content_html":"\u003cp\u003eA parsing vulnerability, identified as CVE-2026-59928, exists within the \u003ccode\u003eblock_parser\u003c/code\u003e component of the open-source Mistune markdown parser library. This flaw allows an attacker to trigger a denial-of-service (DoS) condition in applications utilizing the vulnerable library. The vulnerability arises from an inefficient algorithm that exhibits quadratic-time complexity when processing specially crafted input containing a long list of repeated reference-link definitions. By submitting such malicious input, an attacker can force the \u003ccode\u003eblock_parser\u003c/code\u003e to consume excessive CPU and memory resources, leading to performance degradation, unresponsiveness, or even a crash of the affected application. While no specific threat actors or campaigns are currently associated with the exploitation of this vulnerability, any publicly accessible application using an unpatched version of Mistune could be targeted.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003e\u003cstrong\u003eReconnaissance:\u003c/strong\u003e An attacker identifies a web application or service that utilizes the Mistune markdown parsing library, potentially through version enumeration or public vulnerability databases.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eVulnerability Identification:\u003c/strong\u003e The attacker confirms that the identified application is running a version of Mistune vulnerable to CVE-2026-59928.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003ePayload Crafting:\u003c/strong\u003e The attacker constructs a malicious markdown input containing an extensive number of repeated reference-link definitions specifically designed to exploit the quadratic-time parsing inefficiency.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eInput Delivery:\u003c/strong\u003e The crafted markdown input is submitted to the vulnerable application via a user-controlled input field, API endpoint, or any mechanism that feeds content to the Mistune parser.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eParsing Initiation:\u003c/strong\u003e The vulnerable application receives the malicious input and passes it to the Mistune \u003ccode\u003eblock_parser\u003c/code\u003e component for processing.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eResource Exhaustion:\u003c/strong\u003e During parsing, the \u003ccode\u003eblock_parser\u003c/code\u003e attempts to process the quadratic-time complexity payload, leading to a rapid and exponential increase in CPU and memory utilization.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eDenial of Service:\u003c/strong\u003e The excessive resource consumption causes the application to become unresponsive, slow down significantly, or crash, effectively denying service to legitimate users.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eThe primary impact of successful exploitation of CVE-2026-59928 is a denial-of-service condition for applications that rely on the vulnerable Mistune library. This can lead to significant operational disruptions, service outages, and potential financial losses for organizations whose services become unavailable. Depending on the criticality of the affected application, such outages can impact business continuity, user experience, and public perception. Specific victim counts are not available as this refers to a library vulnerability rather than a widespread campaign, but any unpatched instance could be affected.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003e\u003cstrong\u003ePatch CVE-2026-59928\u003c/strong\u003e by updating the Mistune library to a version that addresses the quadratic-time parsing vulnerability immediately. Consult the official Mistune project or relevant package managers for the latest secure version.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eImplement input validation and sanitization\u003c/strong\u003e for all user-supplied markdown content before it is processed by the Mistune parser to reduce the risk of malicious payloads.\u003c/li\u003e\n\u003cli\u003e\u003cstrong\u003eMonitor application resource utilization\u003c/strong\u003e (CPU, memory) on servers hosting applications that use markdown parsers to detect abnormal spikes that could indicate a DoS attempt.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-07-11T07:40:50Z","date_published":"2026-07-11T07:40:50Z","id":"https://feed.craftedsignal.io/briefs/2026-07-mistune-quadratic-parsing-dos/","summary":"CVE-2026-59928 identifies a vulnerability in the Mistune block_parser component where quadratic-time parsing of long lists of repeated reference-link definitions can be exploited by an attacker to cause a denial-of-service condition due to excessive resource consumption.","title":"CVE-2026-59928 Mistune block_parser: Quadratic-Time Parsing Leading to Denial of Service","url":"https://feed.craftedsignal.io/briefs/2026-07-mistune-quadratic-parsing-dos/"}],"language":"en","title":"CraftedSignal Threat Feed - Mistune Block_parser","version":"https://jsonfeed.org/version/1.1"}