{"id":"CVE-2026-115349","kind":"vulnerability","aliases":["CVE-2026-115349"],"related":[],"title":"Mistune: nested square brackets cause quadratic parsing, exhausting server CPU","description":"Mistune from 3.0.0 before 3.3.0 contains an algorithmic complexity denial of service vulnerability in the parse_link_text function in src/mistune/helpers.py. Attackers can submit markdown with deeply nested square brackets triggering quadratic parsing time, exhausting server CPU with small crafted requests.","summary":"Mistune's parse_link_text function in helpers.py takes quadratic time on markdown with deeply nested square brackets. A small crafted request can tie up server CPU and cause denial of service.","severity":"high","cvss":8.7,"epss":0.00343,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["markdown-rendering","mistune","package","python"],"not_affected_if":["mistune-3.3.0-or-later","mistune-below-3.0.0"],"how_to_check":null,"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":"2026-10-23T22:35:11+00:00","updated_at":"2026-10-24T07:15:51+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-23T22:35:11Z","model":"claude-haiku-5-5","output":{"fix":"Upgrade mistune to 3.3.0 or later.","reach":"internet","title":"Mistune: nested square brackets cause quadratic parsing, exhausting server CPU","impact":"low","summary":"Mistune's parse_link_text function in helpers.py takes quadratic time on markdown with deeply nested square brackets. A small crafted request can tie up server CPU and cause denial of service.","category":"package","who_cares":["python","mistune","markdown-rendering"],"confidence":0.7,"needs_auth":"unknown","worst_case":"Server CPU exhausted by small crafted markdown requests, causing denial of service.","analyst_note":"","how_to_check":"unknown","needs_analyst":false,"not_affected_if":["mistune-below-3.0.0","mistune-3.3.0-or-later"],"user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000453,"input_tokens":2926,"output_tokens":321,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-115349':13A,16A '-2026':12A,15A '3.0.0':57C '3.3.0':59C 'algorithm':62C 'attack':76C 'bracket':4A,40B,84C 'caus':5A,51B 'complex':63C 'contain':60C 'cpu':10A,49B,91C 'craft':43B,94C 'cve':11A,14A 'deepli':37B,81C 'denial':52B,64C 'exhaust':8A,89C 'function':28B,73C 'helpers.py':30B 'link':26B,71C 'markdown':18B,35B,79C 'markdown-rend':17B 'mistun':1A,20B,23B,55C 'nest':2A,38B,82C 'packag':21B 'pars':7A,25B,70C,87C 'python':22B 'quadrat':6A,32B,86C 'render':19B 'request':44B,95C 'server':9A,48B,90C 'servic':54B,66C 'small':42B,93C 'squar':3A,39B,83C 'src/mistune/helpers.py':75C 'submit':78C 'take':31B 'text':27B,72C 'tie':46B 'time':33B,88C 'trigger':85C 'vulner':67C","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-2026-115349","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-115349","severity":null,"published_at":"2026-10-22T19:17:40+00:00","modified_at":"2026-10-22T19:17:40+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-2026-115349","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-115349","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-24T07:15:51+00:00","fetched_at":"2026-10-25T12:38:51+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"}