CVE-2026-44040— UltraVNC 加密问题漏洞

UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes

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.

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

使用具有密码学弱点缺陷的PRNG

UltraVNC 加密问题漏洞

ultravnc是UltraVNC组织开源的一款用于Windows平台的开源远程终端控制软件。 UltraVNC 1.8.2.2及之前版本存在加密问题漏洞，该漏洞源于使用密码学弱的伪随机数生成器生成VNC身份验证挑战字节，在rfb/vncauth.c:119-129中，vncRandomBytes()函数使用time(0) + getpid() + rand()种子libc rand()并生成16字节挑战，组合种子空间约为31位且完全由公开可观察值决定，攻击者可枚举种子空间并在数秒内预测挑战，导致伪造或离

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