Security readout for executives and security teams
Plain-English summary
This flaw can let an unauthenticated network attacker exhaust resources in Siemens HMI, WinCC Runtime Advanced, and listed SINAMICS systems using SmartVNC, causing a denial of service. The business concern is loss of operator visibility or control interface availability, not data theft.
Executive priority
Treat as a high-priority OT availability issue where affected systems support production, safety monitoring, or operator workflows. Prioritize remediation by exposure and process criticality, with special attention to remotely reachable SmartVNC services.
Technical view
SmartVNC has a heap allocation leak in the server Tight encoder. The CVSS 3.1 score is 7.5 with network access, low complexity, no privileges, no user interaction, and high availability impact only. The weakness is mapped to CWE-770.
Likely exposure
Exposure is most likely in OT environments running the listed Siemens SIMATIC HMI panels, WinCC Runtime Advanced V15/V16, or SINAMICS variants, especially where SmartVNC is reachable from broad plant, corporate, or remote-access networks.
Exploitation context
The provided bundle does not show CISA KEV listing or cited evidence of active exploitation. The risk remains operationally significant because the vector is network-reachable, unauthenticated, and targets availability in industrial systems.
Researcher notes
The source bundle identifies many Siemens product lines but only gives explicit fixed thresholds for V15 and V16 HMI and WinCC Runtime Advanced. It does not provide exploit details, active exploitation evidence, or complete remediation detail for SINAMICS all-version entries.
Mitigation direction
- Inventory all listed Siemens HMI, WinCC, and SINAMICS assets.
- Update V15 HMI and WinCC systems to V15.1 Update 6 or later.
- Update V16 HMI and WinCC systems to V16 Update 4 or later.
- For SINAMICS entries marked all versions, follow current Siemens advisory guidance.
- Restrict SmartVNC exposure to trusted management networks only.
- Monitor affected assets for abnormal memory growth or service instability.
Validation and detection
- Compare installed product versions against the affected version ranges.
- Confirm whether SmartVNC is enabled and network-reachable on affected assets.
- Verify untrusted networks cannot reach SmartVNC services.
- Check operational monitoring for denial-of-service symptoms on HMI and drive systems.
- Review Siemens SSA-538778, SSA-286838, and CISA ICSA-21-131-12 for site-specific guidance.
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-770: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-27383 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6CISA-ADPVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- https://cert-portal.siemens.com/productcert/pdf/ssa-538778.pdfCVE reference, siemens · x_refsource_MISC
- https://cert-portal.siemens.com/productcert/pdf/ssa-286838.pdfCVE reference, siemens · x_refsource_MISC
- https://us-cert.cisa.gov/ics/advisories/icsa-21-131-12CVE reference, siemens · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Allocation of Resources Without Limits or Throttling
Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.