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CVE-2026-44042

Estado: ModificadaBaja (3.7)—

UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication. In repeater/webgui/webutils.c:817, the wi_uudecode() function checks whether the input length exceeds the output buffer with a strict greater-than comparison (>), while the correct check should be greater-than-or-equal (>=). When strlen(authdata) equals sizeof(decode), the decoded output length (approximately 3/4 of input) does not overflow the buffer in current practice because the outer HTTP request bounds constrain the Authorization header.

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However, the defective check leaves a latent off-by-one condition that could become exploitable if the buffering constraints change. The current risk is limited to a one-byte write at the boundary of a 1024-byte stack buffer under constrained conditions.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Uvnc — Ultravnc

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-44042",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44042",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-07-01T13:08:54.695763Z"
        }
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    "cvssMetricV31": [
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          "attackVector": "NETWORK",
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          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "LOW",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "NONE"
        },
        "impactScore": 1.4,
        "exploitabilityScore": 2.2
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
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          "versions": [
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              "version": "0",
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              "lessThanOrEqual": "1.8.2.2"
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  "published": "2026-07-01T05:16:21.153",
  "references": [
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      "url": "https://github.com/ultravnc/UltraVNC",
      "tags": [
        "Product"
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      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
    },
    {
      "url": "https://uvnc.com/",
      "tags": [
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        "Release Notes"
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    },
    {
      "url": "https://www.securin.io/zero-days/cve-2026-44042-wi-uudecode-off-by-one-bounded-ultravnc-repeater",
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
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  ],
  "vulnStatus": "Modified",
  "weaknesses": [
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      "type": "Secondary",
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "description": [
        {
          "lang": "en",
          "value": "CWE-193"
        }
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  ],
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      "lang": "en",
      "value": "UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper used for HTTP Basic authentication. In repeater/webgui/webutils.c:817, the wi_uudecode() function checks whether the input length exceeds the output buffer with a strict greater-than comparison (>), while the correct check should be greater-than-or-equal (>=). When strlen(authdata) equals sizeof(decode), the decoded output length (approximately 3/4 of input) does not overflow the buffer in current practice because the outer HTTP request bounds constrain the Authorization header. However, the defective check leaves a latent off-by-one condition that could become exploitable if the buffering constraints change. The current risk is limited to a one-byte write at the boundary of a 1024-byte stack buffer under constrained conditions."
    }
  ],
  "lastModified": "2026-07-09T06:16:21.157",
  "configurations": [
    {
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          "negate": false,
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  "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
}