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CVE-2026-7831— UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing

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.

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及之前版本存在安全漏洞，该漏洞源于在RFB ServerInit消息处理程序中存在栈缓冲区差一错误，当服务器提供的名称长度正好为2024时会导致单字节NUL越界写入，可能触发拒绝服务。需要用户交互（将查看器连接到恶意服务器）。

CVSS 7.5 · High EPSS 0.74% · P53

Affected Version Matrix 1

VendorProduct Version RangeStatus
uvnc UltraVNC ≤ 1.8.2.2 affected
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I. Basic Information for CVE-2026-7831

Vulnerability Information
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Vulnerability Title
UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing
Source: CVE Program / CVE List V5
Vulnerability Description
UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
Off-by-one错误
Source: CVE Program / CVE List V5
Vulnerability Title
UltraVNC 数字错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
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及之前版本存在安全漏洞，该漏洞源于在RFB ServerInit消息处理程序中存在栈缓冲区差一错误，当服务器提供的名称长度正好为2024时会导致单字节NUL越界写入，可能触发拒绝服务。需要用户交互（将查看器连接到恶意服务器）。
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-2026-7831

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Qwen3.6-35B-A3B · 6336 chars
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III. Intelligence Information for CVE-2026-7831

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News Coverage for CVE-2026-7831 (1)

Vendor Pages for CVE-2026-7831 (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-2026-7839 9.1 CRITICAL UltraVNC repeater ships hardcoded default admin password allowing unauthenticated admin ac
CVE-2026-7838 8.8 HIGH UltraVNC viewer heap buffer overflow via integer overflow in RFB connection-failure reason
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-193

V. Comments for CVE-2026-7831

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