Vulnerability-Lookup

GHSA-38W7-MQ68-3H8Q

Vulnerability from github – Published: 2026-07-01 06:31 – Updated: 2026-07-01 06:31

Details

UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.

Severity

7.6 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-7831"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-193"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-01T05:16:24Z",
    "severity": "HIGH"
  },
  "details": "UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.",
  "id": "GHSA-38w7-mq68-3h8q",
  "modified": "2026-07-01T06:31:34Z",
  "published": "2026-07-01T06:31:34Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-7831"
    },
    {
      "type": "WEB",
      "url": "https://github.com/ultravnc/UltraVNC"
    },
    {
      "type": "WEB",
      "url": "https://uvnc.com"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-7831 (GCVE-0-2026-7831)

Vulnerability from cvelistv5 – Published: 2026-07-01 03:33 – Updated: 2026-07-01 13:12

Title

UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing

Summary

Severity

7.5 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-193 - Off-by-one Error
CWE-787 - Out-of-bounds Write

Assigner

securin

References

2 references

URL	Tags
https://uvnc.com/	vendor-advisory
https://github.com/ultravnc/UltraVNC	product

Impacted products

1 product

Vendor	Product	Version
uvnc	UltraVNC	Affected: 0 , ≤ 1.8.2.2 (custom)

Credits

Arjun Basnet, Securin (arjun.basnet@securin.io)

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JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-7831",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-07-01T13:12:22.055256Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-07-01T13:12:46.218Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "modules": [
            "vncviewer"
          ],
          "product": "UltraVNC",
          "vendor": "uvnc",
          "versions": [
            {
              "lessThanOrEqual": "1.8.2.2",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Arjun Basnet, Securin (arjun.basnet@securin.io)"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "LOW",
            "integrityImpact": "LOW",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H",
            "version": "3.1"
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          "scenarios": [
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              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-193",
              "description": "Off-by-one Error",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-787",
              "description": "Out-of-bounds Write",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-07-01T03:33:25.314Z",
        "orgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
        "shortName": "securin"
      },
      "references": [
        {
          "name": "UltraVNC project page",
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://uvnc.com/"
        },
        {
          "name": "UltraVNC source repository",
          "tags": [
            "product"
          ],
          "url": "https://github.com/ultravnc/UltraVNC"
        }
      ],
      "source": {
        "advisory": "Securin Security Advisory \u2014 FINDING-011",
        "discovery": "EXTERNAL"
      },
      "timeline": [
        {
          "lang": "en",
          "time": "2026-06-02T00:00:00.000Z",
          "value": "Vulnerability discovered during security audit"
        },
        {
          "lang": "en",
          "time": "2026-06-17T00:00:00.000Z",
          "value": "Reported to vendor (coordinated disclosure)"
        },
        {
          "lang": "en",
          "time": "2026-09-15T00:00:00.000Z",
          "value": "Planned public disclosure (90-day window)"
        }
      ],
      "title": "UltraVNC viewer off-by-one stack overflow in ServerInit desktop name parsing"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "33c584b5-0579-4c06-b2a0-8d8329fcab9c",
    "assignerShortName": "securin",
    "cveId": "CVE-2026-7831",
    "datePublished": "2026-07-01T03:33:25.314Z",
    "dateReserved": "2026-05-05T04:03:22.622Z",
    "dateUpdated": "2026-07-01T13:12:46.218Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-38W7-MQ68-3H8Q

CVE-2026-7831 (GCVE-0-2026-7831)

Tags

Sightings

Nomenclature