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CVE-2026-44041

Status: ModifiedMedium (6.5)—

UltraVNC through 1.8.2.2 contains an out-of-bounds read in the wide-string to multibyte conversion helper. In rfb/dh.cpp:204, the vncWc2Mb() function passes a caller-supplied WCHAR pointer to wcslen() before any bounds check. If the caller provides a wide-character buffer that is not properly NUL-terminated, wcslen() reads past the end of the buffer until it encounters a NUL wchar, resulting in an out-of-bounds read. Under typical Win32 API usage this requires an abnormal caller contract. Impact is limited to a potential information disclosure from adjacent memory regions or a process crash (denial of service) if the over-read crosses a page boundary.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

Affected technologies (1)

Uvnc — Ultravnc

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2026-44041",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44041",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-07-01T13:10:10.152068Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
        "cvssData": {
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          "version": "3.1",
          "baseScore": 4.3,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "LOW",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 2.8
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
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          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
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      "affectedData": [
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          "modules": [
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            "vncviewer"
          ],
          "product": "UltraVNC",
          "versions": [
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              "status": "affected",
              "version": "0",
              "versionType": "custom",
              "lessThanOrEqual": "1.8.2.2"
            }
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          "defaultStatus": "unaffected"
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  ],
  "published": "2026-07-01T05:16:21.033",
  "references": [
    {
      "url": "https://github.com/ultravnc/UltraVNC",
      "tags": [
        "Product"
      ],
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
    },
    {
      "url": "https://uvnc.com/",
      "tags": [
        "Product",
        "Release Notes"
      ],
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
    },
    {
      "url": "https://www.securin.io/zero-days/cve-2026-44041-vncwc2mb-wcslen-before-bounds-check-ultravnc",
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
    }
  ],
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "description": [
        {
          "lang": "en",
          "value": "CWE-125"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "UltraVNC through 1.8.2.2 contains an out-of-bounds read in the wide-string to multibyte conversion helper. In rfb/dh.cpp:204, the vncWc2Mb() function passes a caller-supplied WCHAR pointer to wcslen() before any bounds check. If the caller provides a wide-character buffer that is not properly NUL-terminated, wcslen() reads past the end of the buffer until it encounters a NUL wchar, resulting in an out-of-bounds read. Under typical Win32 API usage this requires an abnormal caller contract. Impact is limited to a potential information disclosure from adjacent memory regions or a process crash (denial of service) if the over-read crosses a page boundary."
    }
  ],
  "lastModified": "2026-07-09T06:16:21.010",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*",
              "vulnerable": true,
              "matchCriteriaId": "593F7EC1-0922-4652-817A-7D57A0F1210D",
              "versionEndIncluding": "1.8.2.2"
            }
          ],
          "operator": "OR"
        }
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  ],
  "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
}