Vulnerability GHSA-mq36-523m-x7vv

Summary A missing nonce verification in the UserNameIdentityToken authentication handler allows an unauthenticated remote attacker to forge a password token that extracts as an empty string, and to replay captured authentication tokens across sessions.

Affected versions: <= 2.165.0 Tested version: 2.165.0 CVSS Score: 8.1 (High) CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L CWE: CWE-347 Improper Verification of Cryptographic Signature

Proof of Concept (logic, no exploit code)

1. GetEndpoints (unauthenticated) → retrieve server public key and RSA token policy
2. OpenSecureChannel (SecurityMode=None)
3. CreateSession
4. Craft plaintext: [0x20, 0x00, 0x00, 0x00]  (readUInt32LE = 32 = serverNonce.length)
5. RSA-OAEP encrypt with server public key → 256-byte ciphertext
6. ActivateSession with crafted UserNameIdentityToken
7. Server decrypts → length = 32 - 32 = 0 → password = ""
8. isValidUser(username, "") is called

Dynamically confirmed: decryption produces password = "" with no error and no nonce verification.

I am following a 90-day responsible disclosure policy. I am happy to provide additional technical details under embargo. Please confirm receipt at your earliest convenience.

Reporter: Stanley Tobias Discovery date: 2026-03-23