{"id":"CVE-2026-7831","aliases":["EUVD-2026-40883","GHSA-38w7-mq68-3h8q"],"status":"published","title":"UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing","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.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00738,"percentile":0.54864,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-193","CWE-787"],"published":"2026-07-01T03:33:25Z","modified":"2026-10-25T17:10:00Z","products":[{"vendor":"uvnc","product":"ultravnc"}],"references":[{"url":"https://uvnc.com/","tags":["vendor-advisory","Product","Release Notes"]},{"url":"https://github.com/ultravnc/UltraVNC","tags":["product","Product"]},{"url":"https://www.securin.io/zero-days/cve-2026-7831-off-by-one-stack-overflow-viewer-namelength-ultravnc"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-7831"},{"url":"https://uvnc.com"},{"url":"https://github.com/advisories/GHSA-38w7-mq68-3h8q"}],"sources":{"cve":[{"id":"CVE-2026-7831","title":"UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing","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.","status":"published","published":"2026-07-01T03:33:25.314Z","modified":"2026-07-09T04:35:54.891Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-193","CWE-787"],"updated_at":"2026-11-02T14:20:05.830416Z"}],"euvd":[{"id":"EUVD-2026-40883","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.","status":"published","published":"2026-07-01T03:33:25Z","modified":"2026-07-09T04:35:54Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","level":"high"}],"updated_at":"2026-11-02T18:20:04.895477Z"}],"ghsa":[{"id":"GHSA-38w7-mq68-3h8q","title":"UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB...","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.","status":"published","published":"2026-07-01T06:31:34Z","modified":"2026-07-09T06:33:00Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","level":"high"}],"cwes":["CWE-193"],"updated_at":"2026-11-02T15:09:20.981798Z"}],"nvd":[{"id":"CVE-2026-7831","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.","status":"published","published":"2026-07-01T05:16:24.38Z","modified":"2026-10-25T17:10:00.197Z","cvss":[{"version":"3.1","score":7.6,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-193","CWE-787"],"updated_at":"2026-11-02T14:12:27.199837Z"}]}}