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

> A malicious remote peer can trigger a heap buffer overflow in RustDesk's clipboard redirection, potentially allowing arbitrary code execution on the victim's machine.

- **Severity:** High 8.5 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 24 Aug 2026
- **Updated:** 1 Oct 2026
- **Also known as:** GHSA-8m44-j2jr-wmrp

## What is CVE-2026-76840?

CVE-2026-76840 is a high-severity memory corruption vulnerability in rustdesk, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### 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.

Weakness: CWE-787 (Out-of-bounds Write), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2026-76840?


## How do I fix CVE-2026-76840?

No fix has been published for CVE-2026-76840 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-76840 being exploited?

There is no known exploitation of CVE-2026-76840 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-76840 and fix it if it is affected.

What it is: CVE-2026-76840 is a high-severity memory corruption vulnerability in rustdesk, published on 24 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-76840 in the wild and no public exploit code.

Affected product: rustdesk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-76840/ (Markdown: https://insights.sbomify.com/CVE-2026-76840/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-76840
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-76840
- OSV: https://osv.dev/vulnerability/CVE-2026-76840

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-76840/
Summaries are generated and may contain mistakes; the official description above is the record.