{"document":{"category":"csaf_vex","csaf_version":"2.0","title":"CVE-2026-7831: UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing","publisher":{"category":"vendor","name":"HarborGuard Database","namespace":"https://database.harborguard.co"},"tracking":{"id":"CVE-2026-7831","status":"final","version":"1","initial_release_date":"2026-07-01T03:33:25.314Z","current_release_date":"2026-07-01T03:33:25.314Z","revision_history":[{"date":"2026-07-01T03:33:25.314Z","number":"1","summary":"Initial machine-readable export from HarborGuard."}]},"distribution":{"tlp":{"label":"WHITE"},"text":"Public CVE data; freely redistributable."},"notes":[{"category":"description","text":"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.","title":"CVE description"}],"references":[{"category":"self","summary":"CVE-2026-7831 on HarborGuard Database","url":"https://database.harborguard.co/cve/CVE-2026-7831"},{"category":"external","summary":"CVE Record","url":"https://www.cve.org/CVERecord?id=CVE-2026-7831"},{"category":"external","summary":"UltraVNC project page","url":"https://uvnc.com/"},{"category":"external","summary":"UltraVNC source repository","url":"https://github.com/ultravnc/UltraVNC"}]},"product_tree":{"branches":[{"category":"vendor","name":"uvnc","branches":[{"category":"product_name","name":"UltraVNC","branches":[{"category":"product_version_range","name":"<=1.8.2.2","product":{"name":"uvnc UltraVNC <=1.8.2.2","product_id":"CSAFPID-1","product_identification_helper":{"cpe":"cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*"}}}]}]}]},"vulnerabilities":[{"cve":"CVE-2026-7831","title":"UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing","notes":[{"category":"description","text":"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.","title":"CVE description"}],"product_status":{"known_affected":["CSAFPID-1"]},"scores":[{"cvss_v3":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"products":["CSAFPID-1"]}],"remediations":[{"category":"none_available","details":"No fixed version is published yet. Monitor the upstream advisory.","product_ids":["CSAFPID-1"]}]}]}