CVE-2026-7830 UltraVNC MS-Logon II uses 64-bit Diffie-Hellman and seeded libc rand() enabling credential interception

UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme rfbUltraVNCMsLogonIIAuth. In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer DHMAXBITS controls the prime size. A 64-bit DH key can be brok...

CVE-2026-7830 UltraVNC MS-Logon II uses 64-bit Diffie-Hellman and seeded libc rand() enabling credential interception

UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme rfbUltraVNCMsLogonIIAuth. In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer DHMAXBITS controls the prime size. A 64-bit DH key can be brok...

CVE-2026-7830

CVE-2026-7830 affects UltraVNC up to version 1.8.2.2 and concerns the MS-Logon II authentication. The DH key exchange uses parameters within 64-bit space (DH_MAX_BITS) and the private exponent is generated using a rng() that relies on three libc rand() calls seeded from time(NULL). This yields an...

CVE-2026-7830: Inadequate Encryption Strength

UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme rfbUltraVNCMsLogonIIAuth. In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer DHMAXBITS controls the prime size. A 64-bit DH key can be brok...