{"id":"CVE-2026-91039","title":"Authentication Bypass by Spoofing vulnerability in team-alembic ash_authentication allows an attacker who operates one identity-provider connection of a dynamic_oidc strategy to be signed in as a local user established through a differen…","summary":"Authentication Bypass by Spoofing vulnerability in team-alembic ash_authentication allows an attacker who operates one identity-provider connection of a dynamic_oidc strategy to be signed in as a local user established through a differen…","severity":"critical","cvss":9.1,"cvssVector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","cwe":["CWE-290"],"vendor":"team-alembic","product":"ash_authentication","affected":["ash_authentication >= 5.0.0-rc.10 < 5.0.0-rc.14","team-alembic/ash_authentication >= 64530644f9b37ebb76ca14aeb83a77597a0034b7 < 73ad16e452670bbf843550a13361bd41e72ad964"],"published":"2026-09-17","updated":"2026-09-18","sourceUpdated":"2026-09-18T18:16:18.527","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-91039","references":[{"url":"https://cna.erlef.org/cves/CVE-2026-91039.html","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14aeb83a77597a0034b7","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/team-alembic/ash_authentication/commit/73ad16e452670bbf843550a13361bd41e72ad964","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-73j9-m294-fvv9","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-91039","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}],"tags":["nvd","cve.org"],"epss":0.00403,"epssPercentile":0.34311,"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-09-17T19:40:12.687953Z"},"cvssSource":"cna","ingestedAt":"2026-09-17T16:21:47.717Z","slug":"CVE-2026-91039","body":"## Overview\n\nAuthentication Bypass by Spoofing vulnerability in team-alembic ash_authentication allows an attacker who operates one identity-provider connection of a dynamic_oidc strategy to be signed in as a local user established through a different connection.\n\nThe strategy is meant to keep each connection in its own identity namespace by writing every UserIdentity row's strategy field as \"<name>/<connection_id>\", but that namespacing never takes effect. __connection_id__ is populated only on the ephemeral runtime struct built per request in dynamic_oidc/plug.ex, and DynamicOidc.IdentityChange.change/3 re-fetches the strategy from the compile-time DSL through Info.strategy_for_action, yielding the persisted struct whose __connection_id__ is its defstruct default of nil. OAuth2.identity_strategy_name/1 therefore falls back to the bare strategy name for both the identity write and the reads in oauth2/user_resolver.ex and oauth2/sign_in_preparation.ex. Since the identity resource's unique key is (uid, strategy), one row exists per sub across every connection, and the identity-match branch runs before any email check. Neither strategy handles iss, so nothing else distinguishes the issuers: OpenID Connect Core section 5.7 makes sub unique only within an issuer, so two connections numbering subjects independently share one subject space.\n\nThis issue affects ash_authentication: from 5.0.0-rc.10 before 5.0.0-rc.14.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":50,"depthScoreParts":{"impact":50.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}