{"id":"CVE-2026-63398","kind":"vulnerability","aliases":["CVE-2026-63398"],"related":[],"title":"Coop: SAML login can take over another organization's user accounts","description":"Coop is an open source review and moderation tool from ROOST. Prior to 1.0.2, the SAML strategy's verify callback resolved the authenticated user by email alone using `kyselyUserFindByEmail`, without binding the lookup to the organization in `/saml/login/:orgId/callback`. An attacker who administers an organization and controls its SAML IdP signing key can submit an assertion for a victim email to another organization's callback when that target organization has registered the same signing certificate. The assertion verifies against the target certificate, and the email resolves to the target user, creating a session as that user and allowing full cross-tenant account takeover without privileges in the target organization. Exploitation requires the unusual configuration in which the target certificate matches a signing key controlled by the attacker. This issue is fixed in version 1.0.2.","summary":"Coop, an open source moderation tool from ROOST, matches SAML logins by email alone without checking the organization. An attacker who administers one organization and holds a matching SAML signing key can sign in as a user in another organization.","severity":"high","cvss":7.4,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["coop","multi-tenant","package","saml","self-hosted"],"not_affected_if":["no-saml","single-organization","unique-signing-certs","version-1.0.2-or-later"],"how_to_check":"- Check the installed Coop version; it is affected before `1.0.2`.\n- Look for SAML single sign-on configured on more than one organization that shares the same signing certificate.","fix":"- Coop: move to `1.0.2` or later.","status":"open","published_at":"2026-10-30T23:17:14+00:00","first_seen_at":"2026-10-30T23:26:12+00:00","triaged_at":"2026-10-30T23:28:06+00:00","updated_at":"2026-10-30T23:28:06+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-10-30T23:28:06Z","model":"claude-haiku-5-5","output":{"fix":"- Coop: move to `1.0.2` or later.","reach":"network","title":"Coop: SAML login can take over another organization's user accounts","impact":"high","summary":"Coop, an open source moderation tool from ROOST, matches SAML logins by email alone without checking the organization. An attacker who administers one organization and holds a matching SAML signing key can sign in as a user in another organization.","audience":"businesses","category":"package","nicknames":[],"who_cares":["coop","saml","self-hosted","multi-tenant"],"confidence":0.8,"fix_status":"available","needs_auth":"yes","worst_case":"attacker takes over victim accounts in another organization","analyst_note":"","how_to_check":"- Check the installed Coop version; it is affected before `1.0.2`.\n- Look for SAML single sign-on configured on more than one organization that shares the same signing certificate.","plain_action":"","needs_analyst":false,"not_affected_if":["no-saml","single-organization","unique-signing-certs","version-1.0.2-or-later"],"who_is_affected":"Only Coop deployments that use SAML single sign-on, where more than one organization registers the same signing certificate. The attacker must administer one organization and control its signing key. Single-tenant installs or installs without SAML are not exposed.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.000667,"input_tokens":4273,"output_tokens":479,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-63398':14A,17A '/saml/login':104C '1.0.2':80C,201C 'account':11A,169C 'administ':48B,109C 'allow':164C 'alon':40B,93C 'anoth':7A,65B,128C 'assert':122C,143C 'attack':46B,107C,194C 'authent':89C 'bind':97C 'callback':86C,131C 'certif':141C,148C,186C 'check':42B 'configur':181C 'control':113C,191C 'coop':1A,18B,27B,67C 'creat':157C 'cross':167C 'cross-ten':166C 'cve':12A,15A 'email':39B,92C,126C,151C 'exploit':177C 'fix':198C 'full':165C 'hold':52B 'host':26B 'idp':116C 'issu':196C 'key':57B,118C,190C 'kyselyuserfindbyemail':95C 'login':3A,37B 'lookup':99C 'match':35B,54B,187C 'moder':31B,74C 'multi':20B 'multi-ten':19B 'one':49B 'open':29B,70C 'organ':8A,44B,50B,66B,102C,111C,129C,135C,176C 'orgid/callback':105C 'packag':22B 'prior':78C 'privileg':172C 'regist':137C 'requir':178C 'resolv':87C,152C 'review':72C 'roost':34B,77C 'saml':2A,23B,36B,55B,82C,115C 'self':25B 'self-host':24B 'session':159C 'sign':56B,59B,117C,140C,189C 'sourc':30B,71C 'strategi':83C 'submit':120C 'take':5A 'takeov':170C 'target':134C,147C,155C,175C,185C 'tenant':21B,168C 'tool':32B,75C 'unusu':180C 'use':94C 'user':10A,63B,90C,156C,162C 'verifi':85C,144C 'version':200C 'victim':125C 'without':41B,96C,171C","nicknames":[],"mitigations":[],"who_affected":"Only Coop deployments that use SAML single sign-on, where more than one organization registers the same signing certificate. The attacker must administer one organization and control its signing key. Single-tenant installs or installs without SAML are not exposed.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"first_public_at":"2026-10-30T23:17:14+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:N/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":"security-advisories@github.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-63398","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63398","severity":null,"published_at":"2026-10-30T23:17:14+00:00","modified_at":"2026-10-30T23:17:14+00:00","first_seen_at":"2026-10-30T23:26:12+00:00","fetched_at":"2026-10-30T23:26:12+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"}