Insecure Cryptography Vulnerability in UltraVNC by UltraVNC

CVE-2026-7830

What is CVE-2026-7830?

UltraVNC versions up to 1.8.2.2 contain a significant cryptographic vulnerability in the MS-Logon II authentication scheme. The Diffie-Hellman key exchange utilized in this scheme is performed with parameters limited to a 64-bit integer, allowing potential exploitation via Pollard's rho algorithm, which can break a 64-bit DH key in less than a second on modern hardware. Furthermore, the method for generating the private exponent relies on an insecure random number generation process tied to system time, making it vulnerable to passive observers. An attacker with network access could eavesdrop on the MS-Logon II handshake, potentially leading to full credential disclosure as they could decrypt sensitive usernames and passwords.

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