# CVE-2026-76840: RustDesk through 1.4.9 Heap Buffer Overflow via Unvalidated CLIPRDR FileContentsResponse Length

Status: published. Published: 2026-08-24. Updated: 2026-11-08.

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

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/rustdesk/rustdesk/pull/15515

## Affected products and versions

- rustdesk / rustdesk (rustdesk): ≥ 0; ≤ 1.4.9 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.5 (high); 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; source: CNA: VulnCheck

- CVSS 3.1: 9.6 (critical); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:H; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.43% as of 2026-11-08; percentile 37.82%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-787, CWE-20

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/rustdesk/rustdesk (CNA: VulnCheck; product)

- https://github.com/rustdesk/rustdesk/blob/1.4.9/libs/clipboard/src/windows/wf_cliprdr.c (CNA: VulnCheck; technical-description)

- https://github.com/rustdesk/rustdesk/pull/15515 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/FreeRDP/FreeRDP/security/advisories/GHSA-m37j-jcr2-8gcc (CNA: VulnCheck; third-party-advisory, vendor-advisory)

- https://www.vulncheck.com/advisories/rustdesk-through-heap-buffer-overflow-via-unvalidated-cliprdr-filecontentsresponse-length (CNA: VulnCheck; third-party-advisory)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-76840; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-76840; retrieved 2026-11-08; source updated Not reported

Revision: 65eb09f6c91439cd2136270cc67d1fbbdd66fa15d43e4f43c074b56e1010aa3e

Canonical: https://y2.dev/cve/CVE-2026-76840

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