{"id":"CVE-2026-7831","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-7831","generatedAt":"2026-10-28T05:59:24.835Z","title":"UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler.","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.","published":"2026-07-01T05:16:24.000Z","lastModified":"2026-10-25T17:10:00.000Z","status":"Modified","sourceIdentifier":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","cvss":{"version":"3.1","score":7.6,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H"},"cwe":["CWE-193","CWE-787"],"affected":["uvnc/ultravnc"],"epss":{"score":0.00738,"percentile":0.54329,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.74%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://github.com/ultravnc/UltraVNC","tags":["Product"],"source":"33c584b5-0579-4c06-b2a0-8d8329fcab9c"},{"url":"https://uvnc.com/","tags":["Product","Release Notes"],"source":"33c584b5-0579-4c06-b2a0-8d8329fcab9c"},{"url":"https://www.securin.io/zero-days/cve-2026-7831-off-by-one-stack-overflow-viewer-namelength-ultravnc","source":"33c584b5-0579-4c06-b2a0-8d8329fcab9c"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-7831","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}