{
    "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"
                            }
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                ],
                "title": "CISA ADP Vulnrichment",
                "providerMetadata": {
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                    "shortName": "CISA-ADP",
                    "dateUpdated": "2026-07-01T12:33:48.634Z"
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    }
}