Title: Microsoft Windows NT 4.0 PDC/BDC Synchonization Reused Keystream Vulnerability
Severity: HIGH
Description:
In a PDC/BDC synchronization, the entire SAM database is sent encrypted between the Primary and Backup Domain Controllers. A unique RC4 cypher stream is created for each PDC/BDC synchronization. The LM and NT hashes are concatenated for each account and the same cypher stream is applied to each such block of data.
In certain situations where a machine on the network has reset its Trust Account Password, the NT hash will be transmitted normally and the LM hash will be set to contain 16 bytes of zeroes (for the Trust Account only). As any value XORed with all zeroes returns the original value, the second half of the cypher stream is sent over the wire in plaintext in the LM hash field of the Trust Account portion of the synchronization. If an attacker can sniff the data on that segment, it is then possible to decrypt any LM hash from the SAM database using this second half of the keystream.
Affected Products:
- Microsoft Windows NT 4.0
- Microsoft Windows NT Enterprise Server 4.0
- Microsoft Windows NT Server 4.0
- Microsoft Windows NT Terminal Server 4.0
- Microsoft Windows NT Workstation 4.0
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