GitHub Security Advisory: GHSA-gjjc-pcwp-c74m
Package: @oneuptime/common (NPM)
Severity: HIGH (CVSS 8.2)
CWE: CWE-287: Improper Authentication, CWE-294: Authentication Bypass by Capture-replay
Vulnerable versions: <= 10.0.11
Patched in: unpatched

Summary: OneUptime has WebAuthn 2FA bypass: server accepts client-supplied challenge instead of server-stored value, allowing credential replay

Details:
### Summary

The WebAuthn authentication implementation does not store the challenge on the server side. Instead, the challenge is returned to the client and accepted back from the client request body during verification. This violates the WebAuthn specification ([W3C Web Authentication Level 2, §13.4.3](https://www.w3.org/TR/webauthn-2/#sctn-cryptographic-challenges)) and allows an attacker who has obtained a valid WebAuthn assertion (e.g., via XSS, MitM, or log exposure) to replay it indefinitely, completely bypassing the second-factor authentication.

### Details

During WebAuthn authentication, the server generates a random challenge via `generateAuthenticationOptions()` in `Common/Server/Services/UserWebAuthnService.ts` (line 164-221). However, the challenge is **only returned to the client** and **never stored in a session or database** on the server side.

When the client submits the authentication response, the server reads the `expectedChallenge` directly from the untrusted request body (`Authentication.ts:1042`):

```typescript
// App/FeatureSet/Identity/API/Authentication.ts:1041-1049
} else if (verifyWebAuthn) {
  const expectedChallenge: string = data["challenge"] as string;  // ← client-controlled
  const credential: any = data["credential"];

  await UserWebAuthnService.verifyAuthentication({
    userId: alreadySavedUser.id!.toString(),
    challenge: expectedChallenge,  // ← NOT a server-stored value
    credential: credential,
  });
}
```

The `verifyAuthentication()` method then passes this client-provided challenge to `@simplewebauthn/server`'s `verifyAuthenticationResponse()` as `expectedChallenge` (`UserWebAuthnService.ts:268-270`):

```typescript
const verification: any = await verifyAuthenticationResponse({
  response: data.credential,
  expectedChallenge: data.challenge,  // ← client-controlled value used as "expected"
  expectedOrigin: expectedOrigin,
  expectedRPID: Host.toString(),
  credential: { /* public key from DB */ },
});
```

Since both the `expectedChallenge` (from request body) and the challenge embedded in the credential's `clientDataJSON` originate from the same captured assertion, they will always match. The cryptographic signature also remains valid because it was signed by the legitimate user's authenticator.

**Correct flow vs. OneUptime's flow:**

| Step | Correct WebAuthn | OneUptime |
|------|-----------------|-----------|
| 1. Generate challenge | Server generates random challenge | Same |
| 2. Store challenge | **Saved in session/DB** | **Not saved anywhere** |
| 3. Send to client | Sent to client | Same |
| 4. Authenticator signs | Authenticator signs challenge | Same |
| 5. Client returns | Returns signed credential | Returns credential **+ challenge** |
| 6. Verify | Compares against **server-stored** value | Compares against **client-provided** value |
| Result | Replay-proof | **Replayable** |

### PoC

**Prerequisites:**
- An attacker has obtained the victim's password (e.g., credential stuffi