Service interruption via server-side out-of-bounds memory access
Published May 12, 2021 · Updated Jun 2, 2026
Out-of-bounds memory access in Siemens SIMATIC HMI and WinCC products allows remote authenticated users to interrupt service. The SmartVNC server accesses memory beyond a buffer boundary while processing client-sent data; Siemens has not disclosed the affected handler or field. Exploitation requires network access to TCP port 5900, low privileges, and user interaction, and no data disclosure or modification is reported.
Summary
What happened
Out-of-bounds memory access in Siemens SIMATIC HMI and WinCC products allows remote authenticated users to interrupt service. The SmartVNC server accesses memory beyond a buffer boundary while processing client-sent data; Siemens has not disclosed the affected handler or field. Exploitation requires network access to TCP port 5900, low privileges, and user interaction, and no data disclosure or modification is reported.
The record
- CVE
- CVE-2021-25660
- Published
- May 12, 2021
- Updated
- Jun 2, 2026
- Vendor
- Siemens
- Product
- SIMATIC WinCC Runtime Advanced
- Classifications
- CWE-119, CWE-788, T1499.004
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- May 12, 2021CVE publishedPublication date reported by the CVE source.
- Jun 2, 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=All versions < V15.1 Update 6
- Affected versionversion=All versions < V16 Update 4
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
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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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