{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-44040",
        "assignerOrgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
        "state": "PUBLISHED",
        "assignerShortName": "securin",
        "dateReserved": "2026-05-05T03:40:37.003Z",
        "datePublished": "2026-07-01T03:33:20.355Z",
        "dateUpdated": "2026-07-09T04:36:05.643Z"
    },
    "containers": {
        "cna": {
            "title": "UltraVNC vncauth.c uses time-seeded libc rand() to generate VNC authentication challenge bytes",
            "descriptions": [
                {
                    "lang": "en",
                    "value": "UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produce VNC authentication challenge bytes. In rfb/vncauth.c:119-129, the vncRandomBytes() function seeds libc rand() with time(0) + getpid() + rand() and generates a 16-byte challenge. The combined seed space is approximately 31 bits (libc rand() internal state) and is entirely determined by publicly-observable values (wall-clock time and process ID). An attacker who can observe the authentication exchange can enumerate the seed space and predict the challenge within seconds, enabling forgery or offline brute-forcing of responses. Note: on Windows, the active code path may use vncEncryptBytes2.cpp which calls CryptGenRandom; reachability on shipped Windows binaries requires compile-graph verification and is under investigation."
                }
            ],
            "affected": [
                {
                    "vendor": "uvnc",
                    "product": "UltraVNC",
                    "versions": [
                        {
                            "version": "0",
                            "lessThanOrEqual": "1.8.2.2",
                            "status": "affected",
                            "versionType": "custom"
                        }
                    ],
                    "defaultStatus": "unaffected",
                    "modules": [
                        "winvnc",
                        "vncviewer"
                    ]
                }
            ],
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "type": "CWE",
                            "cweId": "CWE-338",
                            "lang": "en",
                            "description": "Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)"
                        }
                    ]
                }
            ],
            "metrics": [
                {
                    "format": "CVSS",
                    "scenarios": [
                        {
                            "lang": "en",
                            "value": "GENERAL"
                        }
                    ],
                    "cvssV3_1": {
                        "version": "3.1",
                        "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
                        "attackVector": "NETWORK",
                        "attackComplexity": "HIGH",
                        "privilegesRequired": "NONE",
                        "userInteraction": "NONE",
                        "scope": "UNCHANGED",
                        "confidentialityImpact": "LOW",
                        "integrityImpact": "LOW",
                        "availabilityImpact": "NONE",
                        "baseScore": 4.8,
                        "baseSeverity": "MEDIUM"
                    }
                }
            ],
            "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-2026-44040-libc-rand-weak-rng-vnc-auth-challenge-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-001"
            },
            "providerMetadata": {
                "orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
                "shortName": "securin",
                "dateUpdated": "2026-07-09T04:36:05.643Z"
            }
        },
        "adp": [
            {
                "metrics": [
                    {
                        "other": {
                            "type": "ssvc",
                            "content": {
                                "timestamp": "2026-07-01T12:44:56.012420Z",
                                "id": "CVE-2026-44040",
                                "options": [
                                    {
                                        "Exploitation": "none"
                                    },
                                    {
                                        "Automatable": "no"
                                    },
                                    {
                                        "Technical Impact": "partial"
                                    }
                                ],
                                "role": "CISA Coordinator",
                                "version": "2.0.3"
                            }
                        }
                    }
                ],
                "title": "CISA ADP Vulnrichment",
                "providerMetadata": {
                    "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
                    "shortName": "CISA-ADP",
                    "dateUpdated": "2026-07-01T12:45:04.706Z"
                }
            }
        ]
    }
}