Service interruption via Tight encoder heap leak
Published May 12, 2021 · Updated Jun 2, 2026
Resource-allocation weakness in Siemens SmartVNC allows remote attackers to interrupt affected HMI services through the VNC interface. The server-side Tight encoder leaks heap allocations while processing attacker-controlled encoding requests, allowing repeated requests to exhaust memory. Sm@rtServer must be enabled and reachable on TCP port 5900; it is disabled by default, and exploitation affects availability without reported data disclosure or modification.
Summary
What happened
Resource-allocation weakness in Siemens SmartVNC allows remote attackers to interrupt affected HMI services through the VNC interface. The server-side Tight encoder leaks heap allocations while processing attacker-controlled encoding requests, allowing repeated requests to exhaust memory. Sm@rtServer must be enabled and reachable on TCP port 5900; it is disabled by default, and exploitation affects availability without reported data disclosure or modification.
The record
- CVE
- CVE-2021-27383
- Published
- May 12, 2021
- Updated
- Jun 2, 2026
- Vendor
- Siemens
- Product
- SINAMICS GM150 (with option X30)
- Classifications
- CWE-770, T0814
- Attack vector
- network
- Privileges
- unauthenticated
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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- Affected versionversion=All versions
What conditions does exploitation require?
What is affected?
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
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Your stack
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