---
id: CVE-2026-76840
title: >-
  RustDesk's Windows clipboard redirection copies a peer-supplied length into a
  fixed-size caller buffer without an upper bound check
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,
  CliprdrSt…
severity: critical
cvss: 9.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:H'
cwe:
  - CWE-20
  - CWE-787
published: '2026-08-24'
updated: '2026-09-23'
sourceUpdated: '2026-09-23T17:17:42.980'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-76840'
references:
  - url: 'https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-m37j-jcr2-8gcc'
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rustdesk/rustdesk'
    label: disclosure@vulncheck.com
  - url: >-
      https://github.com/rustdesk/rustdesk/blob/1.4.9/libs/clipboard/src/windows/wf_cliprdr.c
    label: disclosure@vulncheck.com
  - url: 'https://github.com/rustdesk/rustdesk/pull/15515'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/rustdesk-through-heap-buffer-overflow-via-unvalidated-cliprdr-filecontentsresponse-length
    label: disclosure@vulncheck.com
tags:
  - nvd
epss: 0.00433
epssPercentile: 0.3487
ingestedAt: '2026-09-23T17:28:14.801Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.