RustDesk up to 1.4.9 Clipboard Redirection wf_cliprdr.c CliprdrStream_Read req_fsize heap-based overflow

Summaryinfo

A vulnerability described as critical has been identified in RustDesk up to 1.4.9. This vulnerability affects the function CliprdrStream_Read of the file libs/clipboard/src/windows/wf_cliprdr.c of the component Clipboard Redirection. Executing a manipulation of the argument req_fsize can lead to heap-based overflow. This vulnerability is tracked as CVE-2026-76840. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability has been found in RustDesk up to 1.4.9 and classified as critical. This vulnerability affects the function CliprdrStream_Read of the file libs/clipboard/src/windows/wf_cliprdr.c of the component Clipboard Redirection. The manipulation of the argument req_fsize with an unknown input leads to a heap-based overflow vulnerability. The CWE definition for the vulnerability is CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-76840 since 08/19/2026. The exploitation appears to be easy. The attack can be initiated remotely. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/24/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Name

• RustDesk

Version

• 1.4.0
• 1.4.1
• 1.4.2
• 1.4.3
• 1.4.4
• 1.4.5
• 1.4.6
• 1.4.7
• 1.4.8
• 1.4.9

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