FKIE_CVE-2026-76840

Vulnerability from fkie_nvd - Published: 2026-08-24 14:17 - Updated: 2026-10-14 13:10
Severity
9.6 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:H
Summary
RustDesk's Windows clipboard redirection copies a peer-supplied length into a fixed-size caller buffer without an upper bound check. When an OLE paste consumer such as explorer.exe calls IStream::Read with a buffer of cb bytes, CliprdrStream_Read in libs/clipboard/src/windows/wf_cliprdr.c requests that many bytes of a remote file through cliprdr_send_request_filecontents and then executes CopyMemory(pv, clipboard->req_fdata, clipboard->req_fsize), where req_fsize is taken verbatim from the peer's CLIPRDR FileContentsResponse by wf_cliprdr_server_file_contents_response (req_fsize = fileContentsResponse->cbRequested) and is never clamped to cb anywhere in the chain. The function's only length comparison, req_fsize < cb, handles the short-read case and is evaluated after the copy has already occurred. A malicious or compromised peer that answers a small file-contents read with an oversized response therefore writes attacker-chosen data past the end of the paste consumer's heap buffer when the local user pastes clipboard file contents offered by the remote side. The file is a fork of FreeRDP's client/Windows/wf_cliprdr.c, where the same defect is CVE-2026-68579, fixed in FreeRDP 3.30.0.
References
disclosure@vulncheck.comhttps://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-m37j-jcr2-8gcc
disclosure@vulncheck.comhttps://github.com/rustdesk/rustdesk
disclosure@vulncheck.comhttps://github.com/rustdesk/rustdesk/blob/1.4.9/libs/clipboard/src/windows/wf_cliprdr.c
disclosure@vulncheck.comhttps://github.com/rustdesk/rustdesk/pull/15515
disclosure@vulncheck.comhttps://www.vulncheck.com/advisories/rustdesk-through-heap-buffer-overflow-via-unvalidated-cliprdr-filecontentsresponse-length
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://github.com/rustdesk/rustdesk",
          "defaultStatus": "unaffected",
          "packageName": "rustdesk",
          "product": "rustdesk",
          "vendor": "rustdesk",
          "versions": [
            {
              "lessThanOrEqual": "1.4.9",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "disclosure@vulncheck.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "RustDesk\u0027s Windows clipboard redirection copies a peer-supplied length into a fixed-size caller buffer without an upper bound check. When an OLE paste consumer such as explorer.exe calls IStream::Read with a buffer of cb bytes, CliprdrStream_Read in libs/clipboard/src/windows/wf_cliprdr.c requests that many bytes of a remote file through cliprdr_send_request_filecontents and then executes CopyMemory(pv, clipboard-\u003ereq_fdata, clipboard-\u003ereq_fsize), where req_fsize is taken verbatim from the peer\u0027s CLIPRDR FileContentsResponse by wf_cliprdr_server_file_contents_response (req_fsize = fileContentsResponse-\u003ecbRequested) and is never clamped to cb anywhere in the chain. The function\u0027s only length comparison, req_fsize \u003c cb, handles the short-read case and is evaluated after the copy has already occurred. A malicious or compromised peer that answers a small file-contents read with an oversized response therefore writes attacker-chosen data past the end of the paste consumer\u0027s heap buffer when the local user pastes clipboard file contents offered by the remote side. The file is a fork of FreeRDP\u0027s client/Windows/wf_cliprdr.c, where the same defect is CVE-2026-68579, fixed in FreeRDP 3.30.0."
    },
    {
      "lang": "es",
      "value": "La redirecci\u00f3n del portapapeles de Windows de RustDesk copia una longitud proporcionada por el par en un b\u00fafer de llamador de tama\u00f1o fijo sin una comprobaci\u00f3n de l\u00edmite superior. Cuyo un consumidor de pegado OLE como explorer.exe llama a IStream::Read con un b\u00fafer de cb bytes, CliprdrStream_Read en libs/clipboard/src/windows/wf_cliprdr.c solicita esa cantidad de bytes de un archivo remoto a trav\u00e9s de cliprdr_send_request_filecontents y luego ejecuta CopyMemory(pv, clipboard -\u003e req_fdata, clipboard -\u003e req_fsize), donde req_fsize se toma textualmente de la respuesta CLIPRDR FileContentsResponse del par por wf_cliprdr_server_file_contents_response (req_fsize = fileContentsResponse -\u003e cbRequested) y nunca se ajusta a cb en ning\u00fan lugar de la cadena. La \u00fanica comparaci\u00f3n de longitud de la funci\u00f3n, req_fsize \u003c cb, maneja el caso de lectura corta y se eval\u00faa despu\u00e9s de que la copia ya ha ocurrido. Un par malicioso o comprometido que responde a una lectura peque\u00f1a de contenido de archivo con una respuesta sobredimensionada, por lo tanto, escribe datos elegidos por el atacante m\u00e1s all\u00e1 del final del b\u00fafer de pila del consumidor de pegado cuyo el usuario local pega el contenido del archivo del portapapeles ofrecido por el lado remoto. El archivo es una bifurcaci\u00f3n de client/Windows/wf_cliprdr.c de FreeRDP, donde el mismo defecto es CVE-2026-68579, corregido en FreeRDP 3.30.0."
    }
  ],
  "id": "CVE-2026-76840",
  "lastModified": "2026-10-14T13:10:00.187",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 9.6,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "LOW",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 6.0,
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      }
    ],
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 8.5,
          "baseSeverity": "HIGH",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "HIGH",
          "subConfidentialityImpact": "LOW",
          "subIntegrityImpact": "HIGH",
          "userInteraction": "PASSIVE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:L/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "disclosure@vulncheck.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-76840",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-24T16:26:40.462428Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-24T14:17:01.550",
  "references": [
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-m37j-jcr2-8gcc"
    },
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://github.com/rustdesk/rustdesk"
    },
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://github.com/rustdesk/rustdesk/blob/1.4.9/libs/clipboard/src/windows/wf_cliprdr.c"
    },
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://github.com/rustdesk/rustdesk/pull/15515"
    },
    {
      "source": "disclosure@vulncheck.com",
      "url": "https://www.vulncheck.com/advisories/rustdesk-through-heap-buffer-overflow-via-unvalidated-cliprdr-filecontentsresponse-length"
    }
  ],
  "sourceIdentifier": "disclosure@vulncheck.com",
  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        },
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ],
      "source": "disclosure@vulncheck.com",
      "type": "Secondary"
    }
  ]
}



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