{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-7840","assignerOrgId":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","state":"PUBLISHED","assignerShortName":"securin","dateReserved":"2026-05-05T07:30:59.460Z","datePublished":"2026-07-01T03:33:28.957Z","dateUpdated":"2026-07-09T04:36:16.157Z"},"containers":{"cna":{"title":"UltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE)","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"uvnc","product":"UltraVNC","versions":[{"version":"0","lessThanOrEqual":"1.8.2.2","status":"affected","versionType":"custom"}],"defaultStatus":"unaffected","modules":["repeater"]}],"problemTypes":[{"descriptions":[{"type":"CWE","cweId":"CWE-787","lang":"en","description":"Out-of-bounds Write"}]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH","baseScore":9.8,"baseSeverity":"CRITICAL"},"cvssV4_0":{"version":"4.0","vectorString":"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","baseScore":9.3,"baseSeverity":"CRITICAL"}}],"references":[{"url":"https://uvnc.com/","name":"UltraVNC project page","tags":["vendor-advisory"]},{"url":"https://github.com/ultravnc/UltraVNC","name":"UltraVNC source repository","tags":["product"]},{"url":"https://www.securin.io/zero-days/cve-2026-7840-pre-auth-global-buffer-overflow-repeater-http-admin-ultravnc"}],"timeline":[{"time":"2026-06-02T00:00:00.000Z","lang":"en","value":"Vulnerability discovered during security audit"},{"time":"2026-06-17T00:00:00.000Z","lang":"en","value":"Reported to vendor (coordinated disclosure)"},{"time":"2026-09-15T00:00:00.000Z","lang":"en","value":"Planned public disclosure (90-day window)"}],"credits":[{"lang":"en","value":"Arjun Basnet, Securin (arjun.basnet@securin.io)","type":"finder"}],"source":{"discovery":"EXTERNAL","advisory":"Securin Security Advisory — FINDING-005"},"providerMetadata":{"orgId":"33c584b5-0579-4c06-b2a0-8d8329fcab9c","shortName":"securin","dateUpdated":"2026-07-09T04:36:16.157Z"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-07-01T12:33:40.320112Z","id":"CVE-2026-7840","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-07-01T12:33:48.634Z"}}]}}