Vulnerability · Published Aug 24, 2026 · Assigned by VulnCheck
CVE-2026-76840RustDesk through 1.4.9 Heap Buffer Overflow via Unvalidated CLIPRDR FileContentsResponse Length
Critical 9.6
In plain English
A critical-severity out-of-bounds write in rustdesk from rustdesk. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities).
Official description
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.
Affected products (as reported)
Weakness: CWE-787, CWE-20 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:H
References
- https://github.com/rustdesk/rustdesk product
- https://github.com/rustdesk/rustdesk/blob/1.4.9/libs/clipboard/src/windows/wf_cliprdr.c technical-description
- https://github.com/rustdesk/rustdesk/pull/15515 issue-tracking, patch
- GitHub Security Advisory (GHSA-m37j-jcr2-8gcc) third-party-advisory
- VulnCheck Advisory: RustDesk through 1.4.9 Heap Buffer Overflow via Unvalidated CLIPRDR FileContentsResponse Length third-party-advisory