CVE-2026-44040
MEDIUMUltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes
Title source: cnaExploitation Summary
EIP tracks 1 public exploit for CVE-2026-44040. PoCs published by HermesNA-1.
AI-analyzed exploit summary This repository contains an auto-generated stub module for CVE-2026-44040, describing a cryptographically weak pseudo-random number generator in UltraVNC through 1.8.2.2. The code includes placeholder methods (`check` and `run`) with no actual exploit implementation, only warnings to replace with real PoC code.
Description
UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produce VNC authentication challenge bytes. In rfb/vncauth.c:119-129, the vncRandomBytes() function seeds libc rand() with time(0) + getpid() + rand() and generates a 16-byte challenge. The combined seed space is approximately 31 bits (libc rand() internal state) and is entirely determined by publicly-observable values (wall-clock time and process ID). An attacker who can observe the authentication exchange can enumerate the seed space and predict the challenge within seconds, enabling forgery or offline brute-forcing of responses. Note: on Windows, the active code path may use vncEncryptBytes2.cpp which calls CryptGenRandom; reachability on shipped Windows binaries requires compile-graph verification and is under investigation.
Exploits (1)
This repository contains an auto-generated stub module for CVE-2026-44040, describing a cryptographically weak pseudo-random number generator in UltraVNC through 1.8.2.2. The code includes placeholder methods (`check` and `run`) with no actual exploit implementation, only warnings to replace with real PoC code.
References (3)
Scores
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N