{"schemaVersion":3,"id":"CVE-2026-7840","aliases":[],"status":"published","duplicateOf":null,"title":null,"description":"UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wi_senderr() and wi_replyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf calls. The HTTP receive buffer accepts URIs up to approximately 150 KB (WI_RXBUFSIZE = 153600), so an unauthenticated attacker who can reach the repeater HTTP port (default TCP 80) can overflow hdrbuf by at least 500 bytes with a single HTTP request containing a URI of 1500 bytes or longer, corrupting adjacent .bss-segment globals. The overflow occurs before any authentication check, making it reachable without credentials. A remote, unauthenticated attacker can achieve arbitrary code execution on the host running the repeater.","dates":{"published":"2026-07-01T03:33:28.957Z","modified":"2026-07-09T04:36:16.157Z","reserved":null,"kevAdded":[],"kevDue":[]},"cvss":{"headline":{"score":9.8,"severity":"critical","version":"3.1","versionLabel":"v3.1","source":"NVD","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","computed":false,"selection":"backend-summary"},"metrics":[{"version":"4.0","versionLabel":"v4.0","source":"CVE.org","score":9.3,"severity":"critical","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","exploitability":null,"impact":null,"computed":false},{"version":"4.0","versionLabel":"v4.0","source":"NVD","score":9.3,"severity":"critical","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","exploitability":null,"impact":null,"computed":false},{"version":"3.1","versionLabel":"v3.1","source":"NVD","score":9.8,"severity":"critical","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","exploitability":null,"impact":null,"computed":false}]},"epss":{"probability":0.02628,"percentile":0.85292,"severity":"low","asOf":"2026-10-20T00:00:00.000Z","change":{"pp":0,"baselineDate":"2026-09-20T00:00:00.000Z","baselineScore":0.02628},"history":[{"date":"2026-09-14T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-15T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-16T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-17T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-18T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-19T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-20T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-06T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-07T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-08T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-09T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-10T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-11T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-12T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-13T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-14T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-15T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-16T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-17T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-18T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-19T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-20T00:00:00.000Z","score":0.02628,"percentile":0.85292}],"last30":[{"date":"2026-09-20T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-21T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-22T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-23T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-24T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-25T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-26T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-27T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-28T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-29T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-09-30T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-01T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-02T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-03T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-04T00:00:00.000Z","score":0.02628,"percentile":null},{"date":"2026-10-05T00:00:00.000Z","sc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