CVE-2026-80218

01/Description

Improper Authentication vulnerability in team-alembic AshAuthentication allows an attacker holding a sign-in token for one authenticated resource to be signed in as a user of a different resource. AshAuthentication.Strategy.Password.SignInWithTokenPreparation.extract_primary_keys_from_subject/2 parses the JWT sub claim (for example user?id=1) with URI.parse/1 and keeps only its query string, discarding the path segment that names the subject the token was issued for. Nothing else restores that binding: AshAuthentication.Jwt.verify/3 checks the signature, exp, nbf, jti and the library-version claims, the purpose check only requires sign_in, and the remaining comparison is over primary-key field names, which are identical across resources. The WebAuthn sign-in and remember-me preparations carry copies of the same helper and drop the path in the same way. The magic link sign-in path pins the subject name against the resource and is not affected. This issue affects ash_authentication: from 3.10.5 before 4.15.0 and from 5.0.0-rc.0 before 5.0.0-rc.14.

02/References6

• cna.erlef.org/cves/CVE-2026-80218.html
• github.com/team-alembic/ash_authentication/commit/2640e1872e1fe…
• github.com/team-alembic/ash_authentication/commit/7baac243ca651…
• github.com/team-alembic/ash_authentication/commit/eca8cadea0f15…
• github.com/team-alembic/ash_authentication/security/advisories/…
• osv.dev/vulnerability/EEF-CVE-2026-80218