FKIE_CVE-2026-7829

Vulnerability from fkie_nvd - Published: 2026-07-01 05:16 - Updated: 2026-07-09 06:16
Severity
7.2 (High) - CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
Summary
UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp1[rule1] (25-byte destination) or temp2/temp3 (16-byte destination), the code unconditionally writes a NUL terminator at temp1[rule1][len] = 0 without clamping len to the destination size. When an authenticated administrator saves a rule with a token length equal to or greater than the destination size, the NUL byte is written one or more bytes past the end of the stack-allocated array, corrupting adjacent stack data. An attacker who has obtained admin credentials (including via CVE-2026-7839 default password) can trigger this to gain code execution on the repeater host.
References
33c584b5-0579-4c06-b2a0-8d8329fcab9chttps://github.com/ultravnc/UltraVNCProduct
33c584b5-0579-4c06-b2a0-8d8329fcab9chttps://uvnc.com/Product, Release Notes
33c584b5-0579-4c06-b2a0-8d8329fcab9chttps://www.securin.io/zero-days/cve-2026-7829-post-auth-oob-nul-write-repeater-rule-parser-ultravnc
Impacted products
Vendor Product Version
uvnc ultravnc *
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "modules": [
            "repeater"
          ],
          "product": "UltraVNC",
          "vendor": "uvnc",
          "versions": [
            {
              "lessThanOrEqual": "1.8.2.2",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "593F7EC1-0922-4652-817A-7D57A0F1210D",
              "versionEndIncluding": "1.8.2.2",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the allow/deny rule parser. In repeater/webgui/settings.c:225-272, after strncpy_s copies a rule token into temp1[rule1] (25-byte destination) or temp2/temp3 (16-byte destination), the code unconditionally writes a NUL terminator at temp1[rule1][len] = 0 without clamping len to the destination size. When an authenticated administrator saves a rule with a token length equal to or greater than the destination size, the NUL byte is written one or more bytes past the end of the stack-allocated array, corrupting adjacent stack data. An attacker who has obtained admin credentials (including via CVE-2026-7839 default password) can trigger this to gain code execution on the repeater host."
    }
  ],
  "id": "CVE-2026-7829",
  "lastModified": "2026-07-09T06:16:21.617",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.2,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "HIGH",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.2,
        "impactScore": 5.9,
        "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-7829",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-07-01T13:13:45.463427Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-07-01T05:16:24.087",
  "references": [
    {
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "tags": [
        "Product"
      ],
      "url": "https://github.com/ultravnc/UltraVNC"
    },
    {
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "tags": [
        "Product",
        "Release Notes"
      ],
      "url": "https://uvnc.com/"
    },
    {
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "url": "https://www.securin.io/zero-days/cve-2026-7829-post-auth-oob-nul-write-repeater-rule-parser-ultravnc"
    }
  ],
  "sourceIdentifier": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
  "vulnStatus": "Modified",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ],
      "source": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
      "type": "Secondary"
    }
  ]
}



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