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CVE-2026-7839— UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin access

Quick assessment

Affected
uvnc UltraVNC
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

uvnc UltraVNC是uvnc个人开发者开源的一款Windows远程控制软件。 UltraVNC 1.8.2.2及之前版本存在信任管理问题漏洞，该漏洞源于HTTP管理服务器使用硬编码默认密码初始化，在首次运行时将字符串“adminadmi2”写入为管理员密码，且HTTP基本认证处理程序无速率限制或锁定机制，可导致远程攻击者使用已知默认凭据以管理员身份进行身份验证，从而完全控制中继器配置（包括允许/拒绝规则和会话可见性）。

CVSS 9.1 · Critical EPSS 0.66% · P49

Affected Version Matrix 1

VendorProduct Version RangeStatus
uvnc UltraVNC ≤ 1.8.2.2 affected
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I. Basic Information for CVE-2026-7839

Vulnerability Information
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Vulnerability Title
UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin access
Source: CVE Program / CVE List V5
Vulnerability Description
UltraVNC repeater through 1.8.2.2 initializes the HTTP administration server with a hardcoded default password. In repeater/webgui/settings.c:197, when settings2.txt is absent on first run the repeater writes the literal string "adminadmi2" as the admin password via strcpy_s(saved_password, 64, "adminadmi2"). The HTTP Basic-auth handler wi_decode_auth() checks this password without rate-limiting or lockout. Any remote attacker who can reach the repeater HTTP port (default TCP 80) can authenticate as administrator using the well-known default credential on a fresh or unmodified installation, gaining full control of the repeater configuration including allow/deny rules and session visibility.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用硬编码的凭证
Source: CVE Program / CVE List V5
Vulnerability Title
UltraVNC 信任管理问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
uvnc UltraVNC是uvnc个人开发者开源的一款Windows远程控制软件。 UltraVNC 1.8.2.2及之前版本存在信任管理问题漏洞，该漏洞源于HTTP管理服务器使用硬编码默认密码初始化，在首次运行时将字符串“adminadmi2”写入为管理员密码，且HTTP基本认证处理程序无速率限制或锁定机制，可导致远程攻击者使用已知默认凭据以管理员身份进行身份验证，从而完全控制中继器配置（包括允许/拒绝规则和会话可见性）。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
uvnc UltraVNC 0 ~ 1.8.2.2 -

II. Public POCs for CVE-2026-7839

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 9175 chars
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III. Intelligence Information for CVE-2026-7839

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News Coverage for CVE-2026-7839 (1)

Vendor Pages for CVE-2026-7839 (1)

Same Patch Batch · uvnc · 2026-07-01 · 10 CVEs total

CVE-2026-7840 9.8 CRITICAL UltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE)
CVE-2026-7838 8.8 HIGH UltraVNC viewer heap buffer overflow via integer overflow in RFB connection-failure reason
CVE-2026-7831 7.5 HIGH UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing
CVE-2026-7830 7.4 HIGH UltraVNC MS-Logon II uses 64-bit Diffie-Hellman and seeded libc rand() enabling credential
CVE-2026-7829 7.2 HIGH UltraVNC repeater authenticated out-of-bounds write in rule parser via oversized token
CVE-2026-7828 5.3 MEDIUM UltraVNC repeater integer overflow in win_log malloc leading to heap overflow
CVE-2026-44040 4.8 MEDIUM UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge b
CVE-2026-44041 4.3 MEDIUM UltraVNC vncWc2Mb calls wcslen() before validating that the wide string is NUL-terminated
CVE-2026-44042 3.7 LOW UltraVNC repeater wi_uudecode off-by-one in base64 decode boundary check

IV. Related Vulnerabilities

Same product: UltraVNC
Same vendor: uvnc
Same weakness: CWE-798

V. Comments for CVE-2026-7839

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