Purpose-limited JWT accepted as full bearer authentication in AshAuthentication

Description

Improper Authentication vulnerability in team-alembic AshAuthentication allows purpose-limited JWTs to be replayed as full bearer API credentials when a resource uses stateless bearer-token verification. The bearer-token authentication helper AshAuthentication.Plug.Helpers.retrieve_from_bearer/3 verifies an Authorization: Bearer JWT's signature and rejects tokens containing an act claim, but performs no check that the token's purpose claim equals user at the bearer boundary. When the resource is configured with require_token_presence_for_authentication?: false (the DSL default), the follow-on validate_token/3 helper returns {:ok, nil} without consulting the token resource, so no downstream check on purpose takes place either. As a result, any valid, non-expired JWT the library itself issued for a narrow, single-purpose flow (most notably the purpose: sign_in token that WebAuthn always emits during sign-in, and that the Password strategy emits when sign-in tokens are enabled) is accepted directly as a general-purpose bearer credential and resolves to a full current_user assignment. This bypasses the library's intended token-exchange contract, in which the sign_in token is meant to be presented exactly once to a preparation that validates the purpose claim and immediately revokes the token. The first use of a still-valid sign-in token presented directly in the Authorization header succeeds because the stateless bearer path never scopes it to purpose == "user". An attacker who obtains a not-yet-exchanged sign-in token for a target subject (for example via log or referrer leakage, an intercepted magic-link delivery channel, or a partially compromised intermediary) can present it as a bearer token and be authenticated as that subject, fully bypassing the intended one-time-use and revocation semantics. Exploitation additionally requires that the host application wire up retrieve_from_bearer/3 on a reachable route and uses either WebAuthn (sign-in tokens are always issued) or the Password strategy with sign_in_tokens_enabled?: true. Resources configured with require_token_presence_for_authentication?: true (including applications scaffolded by the Igniter installer since v4.5.0) and the session-based path (authenticate_resource_from_session/4) enforce purpose == "user" against the stored token record and are not affected. This issue affects ash_authentication: from 3.10.5 before 4.14.2 and from 5.0.0-rc.0 before 5.0.0-rc.13.

Timeline

Scores

EPSS (exploitation in 30 days)

0.58% · top 52% of all CVEs (11 Nov 2026)

CISA SSVC

Exploitation: poc · Automatable: no · Technical impact: total

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.6.

Affected products

• team-alembic · ash_authentication

  • affected 3.10.5 – < 4.14.2
  • affected 5.0.0-rc.0 – < 5.0.0-rc.13

• team-alembic · ash_authentication

  • affected eca8cadea0f1595ed2c10a0c177b1da9aa9e5269 – < *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-65322 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-65633](https://cveledger.app/badge/CVE-2026-65633.svg)](https://cveledger.app/cve/CVE-2026-65633)

Record last updated 25 Aug 2026, 19:49 UTC.