Security readout for executives and security teams
Plain-English summary
This Siemens industrial-control vulnerability can let an unauthenticated remote attacker make affected HMI, WinCC Runtime Advanced, or SINAMICS systems unavailable. The impact is denial of service, not data theft or takeover in the provided sources. For plants using these products, the business risk is operational disruption where SmartVNC traffic can reach vulnerable client-side handling.
Executive priority
Treat this as high priority for operational environments because the main risk is loss of availability in industrial systems. Escalate fastest for internet-reachable, flat-network, or production-critical deployments. No active exploitation evidence is provided, so urgency should be exposure-driven rather than incident-driven.
Technical view
CVE-2021-27385 is a CWE-400 resource-consumption flaw in the SmartVNC device layout handler on the client side. Specially crafted network packets can trigger excessive resource use and an infinite-loop denial-of-service condition. CVSS 3.1 is 7.5, with network attack vector, low complexity, no privileges, no user interaction, and high availability impact.
Likely exposure
Exposure is most likely in OT environments using listed Siemens SIMATIC HMI Comfort or KTP Mobile Panels, SIMATIC WinCC Runtime Advanced V15/V16, or listed SINAMICS systems, especially where SmartVNC-related communication is reachable over a network.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. The CVSS vector indicates remote unauthenticated denial of service is plausible when affected SmartVNC handling is reachable, but the sources provided do not establish public exploitation.
Researcher notes
Evidence supports a resource-consumption denial-of-service issue, not confidentiality or integrity impact. The affected list is broad and includes some products marked all versions affected. The bundle provides fixed thresholds for SIMATIC HMI and WinCC V15/V16, but not a universal fix statement for every SINAMICS entry.
Mitigation direction
- Upgrade affected SIMATIC HMI and WinCC Runtime Advanced deployments to the fixed update levels named by Siemens/CVE data.
- For SINAMICS products listed as all versions affected, check Siemens advisories for product-specific remediation or workarounds.
- Restrict network reachability to SmartVNC-related services to trusted operational networks only.
- Prioritize compensating controls where affected systems support safety-critical or production-critical operations.
Validation and detection
- Inventory Siemens products against the affected product and version list in the CVE record.
- Confirm SIMATIC HMI and WinCC Runtime Advanced versions meet or exceed the named fixed update levels.
- Identify SINAMICS GH150, GL150 X30, GM150 X30, SH150, SL150, SM120, SM150, and SM150i deployments.
- Review network paths to determine whether SmartVNC-related communication is reachable from untrusted segments.
Public sources used
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-400: 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-2021-27385 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.
Uncontrolled Resource Consumption
Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.