{"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": "2026-07-01T03:33:28.957Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c", "shortName": "securin", "dateUpdated": "2026-07-01T03:33:28.957Z"}, "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"]}], "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 ([email protected])", "type": "finder"}], "source": {"discovery": "EXTERNAL", "advisory": "Securin Security Advisory \u2014 FINDING-005"}}}}

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