{"id":"CVE-2026-116578","kind":"vulnerability","aliases":["CVE-2026-116578"],"related":[],"title":"Tornado: RedirectHandler templates let crafted paths send users to other sites","description":"Tornado is a Python web framework and asynchronous networking library. Prior to 6.6, tornado.web.RedirectHandler URL templates can place regex-capture substitutions where crafted request paths change the redirect scheme or network location. Affected placements include substitutions at the start of a path, directly after a fixed host, or at the beginning of the template, including protocol-relative, absolute, backslash, encoded, host-extension, and user-info variants interpreted by browsers as attacker-controlled destinations. Static templates and substitutions after a fixed host followed by a slash are not affected. An attacker can use the resulting open redirect on the application's domain for phishing. This issue is fixed in version 6.6.","summary":"Tornado's RedirectHandler can be given URL templates with regex-capture substitutions in positions that let a crafted request path change the redirect scheme or host. An attacker gets an open redirect on the application's own domain, usable for phishing.","severity":"low","cvss":2.1,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["package","python","self-hosted","tornado"],"not_affected_if":["no-redirecthandler","static-redirect-templates","upgraded-to-6.6"],"how_to_check":"- `pip show tornado` or `python -c \"import tornado; print(tornado.version)\"` to read the installed version\n- Search the codebase for `RedirectHandler` and check whether any URL template starts with a regex capture group, or places one directly after a fixed host","fix":"- Upgrade tornado to `6.6` or later\n- Where upgrading is not possible, make redirect templates static or keep a slash after any fixed host before a capture group","status":"open","published_at":"2026-10-26T21:18:14+00:00","first_seen_at":"2026-10-26T21:20:31+00:00","triaged_at":"2026-10-26T21:21:20+00:00","updated_at":"2026-10-26T21:21:20+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-26T21:21:20Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade tornado to `6.6` or later\n- Where upgrading is not possible, make redirect templates static or keep a slash after any fixed host before a capture group","reach":"internet","title":"Tornado: RedirectHandler templates let crafted paths send users to other sites","impact":"low","summary":"Tornado's RedirectHandler can be given URL templates with regex-capture substitutions in positions that let a crafted request path change the redirect scheme or host. An attacker gets an open redirect on the application's own domain, usable for phishing.","category":"package","nicknames":[],"who_cares":["python","tornado","self-hosted"],"confidence":0.7,"needs_auth":"no","worst_case":"users are redirected to attacker-chosen sites from the app's domain","analyst_note":"","how_to_check":"- `pip show tornado` or `python -c \"import tornado; print(tornado.version)\"` to read the installed version\n- Search the codebase for `RedirectHandler` and check whether any URL template starts with a regex capture group, or places one directly after a fixed host","needs_analyst":false,"not_affected_if":["static-redirect-templates","no-redirecthandler","upgraded-to-6.6"],"who_is_affected":"Applications that use tornado.web.RedirectHandler with a URL template where a regex capture group sits at the start of the template, directly after a fixed host, or at the start of a path. Static redirect templates and templates with a slash after the fixed host are not affected.","user_interaction":"yes","needs_special_setup":"yes","severity_if_unknown":"low"},"cost_usd":0.000614,"input_tokens":3428,"output_tokens":543,"severity_before":"low"},"analyst_status":null,"analyst_note":null,"search":"'-116578':14A,17A '-2026':13A,16A '6.6':78C,180C 'absolut':125C 'affect':99C,158C 'applic':59B,169C 'asynchron':73C 'attack':52B,141C,160C 'attacker-control':140C 'backslash':126C 'begin':117C 'browser':138C 'captur':35B,86C 'chang':45B,92C 'control':142C 'craft':5A,42B,89C 'cve':12A,15A 'destin':143C 'direct':109C 'domain':62B,171C 'encod':127C 'extens':130C 'fix':112C,150C,177C 'follow':152C 'framework':71C 'get':53B 'given':29B 'host':22B,50B,113C,129C,151C 'host-extens':128C 'includ':101C,121C 'info':134C 'interpret':136C 'issu':175C 'let':4A,40B 'librari':75C 'locat':98C 'network':74C,97C 'open':55B,165C 'packag':18B 'path':6A,44B,91C,108C 'phish':65B,173C 'place':83C 'placement':100C 'posit':38B 'prior':76C 'protocol':123C 'protocol-rel':122C 'python':19B,69C 'redirect':47B,56B,94C,166C 'redirecthandl':2A,26B 'regex':34B,85C 'regex-captur':33B,84C 'relat':124C 'request':43B,90C 'result':164C 'scheme':48B,95C 'self':21B 'self-host':20B 'send':7A 'site':11A 'slash':155C 'start':105C 'static':144C 'substitut':36B,87C,102C,147C 'templat':3A,31B,81C,120C,145C 'tornado':1A,23B,24B,66C 'tornado.web.redirecthandler':79C 'url':30B,80C 'usabl':63B 'use':162C 'user':8A,133C 'user-info':132C 'variant':135C 'version':179C 'web':70C","nicknames":[],"mitigations":[],"who_affected":"Applications that use tornado.web.RedirectHandler with a URL template where a regex capture group sits at the start of the template, directly after a fixed host, or at the start of a path. Static redirect templates and templates with a slash after the fixed host are not affected.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-26T21:18:14+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:N/SI:L/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":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-116578","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-116578","severity":null,"published_at":"2026-10-26T21:18:14+00:00","modified_at":"2026-10-26T21:18:15+00:00","first_seen_at":"2026-10-26T21:20:31+00:00","fetched_at":"2026-10-26T21:20:31+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"}