{"id":"CVE-2026-114617","kind":"vulnerability","aliases":["CVE-2026-114617"],"related":[],"title":"Authlib: ID token replay possible when nonce check is skipped","description":"Authlib is a Python library which builds OAuth and OpenID Connect servers. Prior to 1.9.0, OpenIDMixin.parse_id_token() reads the nonce_supported decision from the untrusted ID token being validated and sets the expected nonce to null when that claim is the JSON boolean false. In implicit and hybrid relying parties, or applications that directly accept externally supplied ID tokens, an attacker with a captured validly signed token can bypass the nonce-to-session binding and replay the victim's token into an attacker-controlled session. Plain authorization code flow is not affected, and the token must still pass signature, issuer, and audience validation. OpenIDMixin.parse_id_token() trusts nonce_supported in both authlib/integrations/base_client/sync_openid.py and authlib/integrations/base_client/async_openid.py to disable the expected nonce. This issue is fixed in version 1.9.0.","summary":"Authlib's OpenID Connect parser lets a token disable its own nonce check by setting nonce_supported to false. An attacker holding a validly signed ID token can replay it into their own session in implicit and hybrid flows.","severity":"medium","cvss":4.2,"epss":0.00188,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["authlib","oauth","openid-connect","package","python"],"not_affected_if":["authorization-code-flow-only","no-external-id-tokens"],"how_to_check":"- Run `pip show authlib` and check the installed version is below `1.9.0`\n- Search requirements or lock files for `authlib` to find pinned versions\n- Check whether the app uses implicit or hybrid OpenID Connect flows, or accepts externally supplied ID tokens","fix":"- Upgrade Authlib to `1.9.0` or later\n- Until upgraded, avoid implicit and hybrid flows and do not accept externally supplied ID tokens","status":"open","published_at":"2026-10-22T22:18:04+00:00","first_seen_at":"2026-10-23T21:57:32+00:00","triaged_at":"2026-10-25T04:41:21+00:00","updated_at":"2026-10-25T04:41:21+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-10-25T04:41:21Z","model":"claude-haiku-5-5","output":{"fix":"- Upgrade Authlib to `1.9.0` or later\n- Until upgraded, avoid implicit and hybrid flows and do not accept externally supplied ID tokens","reach":"internet","title":"Authlib: ID token replay possible when nonce check is skipped","impact":"medium","summary":"Authlib's OpenID Connect parser lets a token disable its own nonce check by setting nonce_supported to false. An attacker holding a validly signed ID token can replay it into their own session in implicit and hybrid flows.","category":"package","nicknames":[],"who_cares":["python","authlib","oauth","openid-connect"],"confidence":0.7,"needs_auth":"unknown","worst_case":"attacker replays a victim's ID token into their own session","analyst_note":"","how_to_check":"- Run `pip show authlib` and check the installed version is below `1.9.0`\n- Search requirements or lock files for `authlib` to find pinned versions\n- Check whether the app uses implicit or hybrid OpenID Connect flows, or accepts externally supplied ID tokens","needs_analyst":false,"not_affected_if":["authorization-code-flow-only","no-external-id-tokens"],"who_is_affected":"Applications that use Authlib's OpenIDMixin.parse_id_token() with implicit or hybrid OpenID Connect relying parties, or that directly accept ID tokens supplied from outside. Plain authorization code flow is not affected, and the token must still pass signature, issuer and audience checks.","user_interaction":"unknown","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.000634,"input_tokens":3552,"output_tokens":557,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-114617':13A,16A '-2026':12A,15A '1.9.0':77C,191C 'accept':118C 'affect':157C 'applic':115C 'attack':44B,124C,148C 'attacker-control':147C 'audienc':167C 'authlib':1A,17B,24B,63C 'authlib/integrations/base_client/async_openid.py':179C 'authlib/integrations/base_client/sync_openid.py':177C 'author':152C 'bind':138C 'boolean':106C 'build':69C 'bypass':132C 'captur':127C 'check':8A,36B 'claim':102C 'code':153C 'connect':21B,27B,73C 'control':149C 'cve':11A,14A 'decis':85C 'direct':117C 'disabl':32B,181C 'expect':96C,183C 'extern':119C 'fals':42B,107C 'fix':188C 'flow':62B,154C 'hold':45B 'hybrid':61B,111C 'id':2A,49B,79C,89C,121C,170C 'implicit':59B,109C 'issu':186C 'issuer':165C 'json':105C 'let':29B 'librari':67C 'must':161C 'nonc':7A,35B,39B,83C,97C,135C,173C,184C 'nonce-to-sess':134C 'null':99C 'oauth':18B,70C 'openid':20B,26B,72C 'openid-connect':19B 'openidmixin.parse':78C,169C 'packag':22B 'parser':28B 'parti':113C 'pass':163C 'plain':151C 'possibl':5A 'prior':75C 'python':23B,66C 'read':81C 'reli':112C 'replay':4A,52B,140C 'server':74C 'session':57B,137C,150C 'set':38B,94C 'sign':48B,129C 'signatur':164C 'skip':10A 'still':162C 'suppli':120C 'support':40B,84C,174C 'token':3A,31B,50B,80C,90C,122C,130C,144C,160C,171C 'trust':172C 'untrust':88C 'valid':47B,92C,128C,168C 'version':190C 'victim':142C","nicknames":[],"mitigations":[],"who_affected":"Applications that use Authlib's OpenIDMixin.parse_id_token() with implicit or hybrid OpenID Connect relying parties, or that directly accept ID tokens supplied from outside. Plain authorization code flow is not affected, and the token must still pass signature, issuer and audience checks.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-22T22:18:04+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N","cvss_by":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-114617","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-114617","severity":null,"published_at":"2026-10-22T22:18:04+00:00","modified_at":"2026-10-23T19:34:14+00:00","first_seen_at":"2026-10-23T21:57:32+00:00","fetched_at":"2026-10-23T22:29:03+00:00","note":null},{"source":"epss","external_id":"CVE-2026-114617","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-114617","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"}