Ech0 before 4.7.3 OAuth Redirect URI Validation Bypass

Summary

Ech0 through 4.5.6 contains an OAuth redirect URI validation vulnerability in parseAndValidateClientRedirect (internal/service/auth/auth.go) that compares only the scheme and host of the client-supplied redirect_uri against the admin-configured allowlist, ignoring path, query, and fragment components. The redirect_uri is embedded into the signed state JWT at login time without validation. An attacker can craft a redirect_uri whose host matches an allowed origin but whose path is attacker-influenced; after the OAuth exchange the victim is redirected to that path with a one-time exchange code in the query string. If the code leaks (e.g., via Referer, analytics, or an open redirect on that host), the attacker can trade it at the public POST /api/auth/exchange endpoint for the victim's access and refresh tokens. Fixed in 4.7.3.

Timeline

1. Aug 25, 2026, 11:33 AM UTCCVE published
2. Aug 25, 2026, 2:30 PM UTCCISA SSVC assessment

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

3. Aug 25, 2026, 2:51 PM UTCRecord last updated

Affected versions

• lin-snow Ech0

  fixed in 4.7.3

• github.com/lin-snow/Ech0Go

  fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1

• github.com/lin-snow/ech0Go

  fixed in 1.4.8-0.20260503040728-a7e8b8e84bd1

References 2