Remote code execution via RDP payload size overflow
Published Aug 12, 2021 · Updated Aug 10, 2026
Heap buffer overflow in Microsoft Remote Desktop Client allows remote attackers to execute code when a user connects to a malicious RDP server. In mstscax.dll, an attacker-controlled RDP Video Redirection payload-size field overflows an allocation calculation, leaving a heap buffer too small for the decompressed data. Exploitation requires user interaction with the malicious server and grants code execution in the affected client process.
Summary
What happened
Heap buffer overflow in Microsoft Remote Desktop Client allows remote attackers to execute code when a user connects to a malicious RDP server. In mstscax.dll, an attacker-controlled RDP Video Redirection payload-size field overflows an allocation calculation, leaving a heap buffer too small for the decompressed data. Exploitation requires user interaction with the malicious server and grants code execution in the affected client process.
The record
- CVE
- CVE-2021-34535
- Published
- Aug 12, 2021
- Updated
- Aug 10, 2026
- Vendor
- Microsoft
- Product
- Windows 10 Version 1507
- Classifications
- T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 12, 2021CVE publishedPublication date reported by the CVE source.
- Aug 10, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.10240.0 <10.0.10240.19022
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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