{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/products/commonmark/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["commonmark"],"_cs_severities":["medium"],"_cs_tags":[],"_cs_type":"advisory","_cs_vendors":[],"content_html":"\u003cp\u003eThe league/commonmark library, a popular PHP Markdown parser, is vulnerable to a denial of service (DoS) flaw (CVE-2026-71488) due to quadratic time complexity during the parsing of specifically crafted Markdown lines. The library improperly handles the translation between character positions and byte positions when processing UTF-8 multibyte characters. By including a single non-ASCII character in a long line containing repeated punctuation or whitespace, an attacker triggers a rescan of the growing string, forcing the parser into an increasingly inefficient state.\u003c/p\u003e\n\u003cp\u003eFurthermore, the Autolink extension exhibits similar performance degradation by repeatedly copying and validating the remaining line for every URL-like prefix identified. This vulnerability affects versions 0.6.0 through 2.8.3, including standard \u003ccode\u003eCommonMarkConverter\u003c/code\u003e and \u003ccode\u003eGithubFlavoredMarkdownConverter\u003c/code\u003e instances. An attacker submitting maliciously crafted Markdown to a web application can consume disproportionate CPU and memory resources, leading to the exhaustion of PHP workers and service-wide denial of service. The vulnerability is limited to availability and does not permit data disclosure or unauthorized execution.\u003c/p\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eSuccessful exploitation results in service unavailability by saturating PHP worker processes. Because the computationally expensive work occurs before HTML rendering, existing security configurations like \u003ccode\u003ehtml_input\u003c/code\u003e settings do not mitigate the issue. Applications processing untrusted Markdown from public users are at high risk. The complexity of the attack is low, as a single request containing a long, crafted line is sufficient to trigger the resource exhaustion, and no complex Markdown structure is required.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cp\u003ePrioritized, concrete actions for detection engineering and development teams:\u003c/p\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade \u003ccode\u003eleague/commonmark\u003c/code\u003e to version 2.9.0 or later immediately to resolve the underlying algorithmic flaw in character-to-byte position conversion.\u003c/li\u003e\n\u003cli\u003eImplement strict input validation to truncate or reject individual Markdown lines that exceed reasonable length limits before passing them to the parser.\u003c/li\u003e\n\u003cli\u003eConfigure application-level request limits and rate limiting to prevent concurrent abuse of the parsing engine.\u003c/li\u003e\n\u003cli\u003eApply PHP execution-time limits to ensure individual process requests cannot hang indefinitely during expensive parsing operations.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-08-06T21:29:44Z","date_published":"2026-08-06T21:29:44Z","id":"https://feed.craftedsignal.io/briefs/2026-08-commonmark-dos/","summary":"The league/commonmark library is susceptible to a denial of service vulnerability via crafted Markdown inputs that cause excessive CPU usage and resource exhaustion due to inefficient multibyte character processing.","title":"Quadratic-time Denial of Service in league/commonmark","url":"https://feed.craftedsignal.io/briefs/2026-08-commonmark-dos/"}],"language":"en","title":"CraftedSignal Threat Feed - Commonmark","version":"https://jsonfeed.org/version/1.1"}