{"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":0.003,"epssPercentile":0.22863,"ingestedAt":"2026-09-23T17:28:14.801Z","slug":"CVE-2026-76840","body":"## Overview\n\nRustDesk'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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":53,"depthScoreParts":{"impact":52.8,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}