{"id":"CVE-2026-115348","kind":"vulnerability","aliases":["CVE-2026-115348"],"related":[],"title":"Mistune: crafted Markdown with unbalanced brackets exhausts server CPU","description":"Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity vulnerability in the inline link parser's parse_link_text function that allows unauthenticated attackers to exhaust CPU with unbalanced brackets. Attackers can submit Markdown containing many unbalanced '[' or '![' characters, forcing repeated unbounded forward scans and tying up worker processes for minutes.","summary":"Mistune, a Python Markdown parser, has an algorithmic complexity flaw in its inline link parser. An unauthenticated attacker can send Markdown with many unbalanced '[' or '![' characters to tie up worker processes for minutes.","severity":"high","cvss":8.7,"epss":0.00359,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["markdown-rendering","mistune","package","python","self-hosted"],"not_affected_if":["mistune-not-installed","no-user-markdown-input","version-3.3.0-or-later"],"how_to_check":"pip show mistune (or check the installed version in your lockfile) and see whether it is between 3.0.0 and 3.2.x.","fix":"Upgrade mistune to 3.3.0 or later.","status":"open","published_at":"2026-10-22T19:17:40+00:00","first_seen_at":"2026-10-23T21:57:31+00:00","triaged_at":"2026-10-23T22:35:12+00:00","updated_at":"2026-10-24T07:15:51+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-10-23T22:35:12Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade mistune to 3.3.0 or later.","reach":"internet","title":"Mistune: crafted Markdown with unbalanced brackets exhausts server CPU","impact":"low","summary":"Mistune, a Python Markdown parser, has an algorithmic complexity flaw in its inline link parser. An unauthenticated attacker can send Markdown with many unbalanced '[' or '![' characters to tie up worker processes for minutes.","category":"package","who_cares":["python","mistune","markdown-rendering","self-hosted"],"confidence":0.8,"needs_auth":"no","worst_case":"Worker processes are pinned on CPU, causing denial of service.","analyst_note":"","how_to_check":"pip show mistune (or check the installed version in your lockfile) and see whether it is between 3.0.0 and 3.2.x.","needs_analyst":false,"not_affected_if":["mistune-not-installed","version-3.3.0-or-later","no-user-markdown-input"],"user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"high"},"cost_usd":0.000486,"input_tokens":2955,"output_tokens":380,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-115348':12A,15A '-2026':11A,14A '3.0.0':60C '3.3.0':62C 'algorithm':32B,65C 'allow':79C 'attack':42B,81C,88C 'bracket':6A,87C 'charact':50B,96C 'complex':33B,66C 'contain':63C,92C 'cpu':9A,84C 'craft':2A 'cve':10A,13A 'exhaust':7A,83C 'flaw':34B 'forc':97C 'forward':100C 'function':77C 'host':24B 'inlin':37B,70C 'link':38B,71C,75C 'mani':47B,93C 'markdown':3A,17B,28B,45B,91C 'markdown-rend':16B 'minut':57B,108C 'mistun':1A,19B,25B,58C 'packag':20B 'pars':74C 'parser':29B,39B,72C 'process':55B,106C 'python':21B,27B 'render':18B 'repeat':98C 'scan':101C 'self':23B 'self-host':22B 'send':44B 'server':8A 'submit':90C 'text':76C 'tie':52B,103C 'unauthent':41B,80C 'unbalanc':5A,48B,86C,94C 'unbound':99C 'vulner':67C 'worker':54B,105C","nicknames":[],"mitigations":[],"who_affected":null,"tier":"B","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-22T19:17:40+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-115348","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115348","severity":null,"published_at":"2026-10-22T19:17:40+00:00","modified_at":"2026-10-23T21:17:21+00:00","first_seen_at":"2026-10-23T21:57:31+00:00","fetched_at":"2026-10-23T22:29:02+00:00","note":null},{"source":"epss","external_id":"CVE-2026-115348","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-115348","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-24T07:15:51+00:00","fetched_at":"2026-10-24T07:15:51+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}