CVE detail
CVE-2026-7830
UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme (rfbUltraVNC_MsLogonIIAuth). In rfb/dh.cpp the Diffie-Hellman key exchange is performed with parameters that fit in an unsigned 64-bit integer (DH_MAX_BITS controls the prime size). A 64-bit DH key can be broken by Pollard's rho algorithm in under one second on current hardware. Additionally, the private exponent is generated by the rng() function, which multiplies three libc rand() values seeded from time(NULL). With approximately 31 bits of internal state and a time-based seed, the private exponent is recoverable in under a minute by a passive observer. A network attacker who can observe the MS-Logon II handshake (via sniffing, recording, or man-in-the-middle) can derive the shared DH key and decrypt the encapsulated username and password, resulting in full credential disclosure. This affects legacy MS-Logon II connections; MS-Logon III (X25519 + AES-256-GCM) is unaffected.
Buzz score
Why this CVE is surfacing
This all-time snapshot uses the same composite formula as Trending across a 30-year evidence window, rather than a current rolling window.
Buzz score components · mention 13.9 · diversity 11.5 · KEV 0.0 · OTX 0.0 · PoC 0.0
Why it matters now
Mention timeline
- Total mentions
- 3
- within the 30d window
- Peak daily
- 3
- highest bucket
Evidence
Source links by recency
3 source links · newest first
- https://www.securin.io/zero-days/cve-2026-7830-31-bit-dh-weak-rng-ms-logon-credential-interception-ultravncwww.securin.io
No excerpt available.
Exploitwww.securin.ioJul 1, 2026, 5:16 AM - https://uvnc.com/uvnc.com
No excerpt available.
Release Notesuvnc.comJul 1, 2026, 5:16 AM - https://github.com/ultravnc/UltraVNCgithub.com
No excerpt available.
Exploitgithub.comJul 1, 2026, 5:16 AM
Exploit code
Public exploit repository references
Public PoC repositories are third-party, potentially unsafe artifacts. Treat their code as untrusted and use it only on authorized systems in an isolated, least-privilege environment. cvebuzz does not execute the code or verify that an exploit works.
0 repository references · best confidence N/A · max 0 stars
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