Security readout for executives and security teams
Plain-English summary
This Siemens industrial-control issue can let an unauthenticated network attacker crash affected PLCs by sending malformed traffic to TCP port 102. The business impact is operational disruption: affected automation controllers may stop functioning until restarted. It is high priority where these devices control production, utilities, or safety-adjacent processes.
Executive priority
Treat as high priority for facilities where Siemens PLC downtime can interrupt operations. Prioritize exposed or poorly segmented controllers first, then complete version validation and remediation tracking across OT assets.
Technical view
CVE-2021-37204 affects multiple Siemens SIMATIC and SIPLUS controller families and S7-PLCSIM Advanced versions. The flaw is CWE-672 and has CVSS 3.1 score 7.5. Attack vector is network, low complexity, no privileges, no user interaction, with high availability impact and no confidentiality or integrity impact stated.
Likely exposure
Exposure is most relevant in OT networks where affected Siemens controllers or simulation software are reachable on TCP/102. Internet exposure would materially raise risk, but the provided sources do not state how commonly exposed these devices are.
Exploitation context
The source bundle does not show CISA KEV listing or confirmed active exploitation. It states proof-of-concept maturity in CVSS and describes unauthenticated denial of service over TCP/102, requiring device restart to restore normal operations.
Researcher notes
The vulnerability is availability-only in the provided data. Do not assume code execution or data compromise. The advisory identifies many product families with distinct affected version ranges, so validation should be product-specific rather than based on the SIMATIC brand alone.
Mitigation direction
- Apply Siemens ProductCERT guidance in SSA-838121 for each affected product and version.
- Upgrade affected products to non-affected versions where Siemens provides them.
- Restrict TCP/102 access to trusted engineering stations and required automation peers.
- Isolate PLC networks from enterprise and internet-facing networks.
- For products listed as all versions affected, check Siemens guidance for current remediation status.
- Prepare operational restart procedures for affected devices after a denial-of-service event.
Validation and detection
- Inventory Siemens SIMATIC and SIPLUS assets, including software controllers and S7-PLCSIM Advanced.
- Compare firmware or software versions against the affected ranges in the advisory.
- Verify TCP/102 is not reachable from untrusted networks.
- Review firewall and segmentation rules protecting engineering and PLC networks.
- Confirm Siemens advisory SSA-838121 has been applied or tracked as an exception.
- Check monitoring for unexpected PLC restarts, communication loss, or port 102 anomalies.
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-672: 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-2021-37204 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/E:P/RL:O/RC:C
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.
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:H/E:P/RL:O/RC:C3.93.6Primary CVE scoreVulnerability 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/E:P/RL:O/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- https://cert-portal.siemens.com/productcert/pdf/ssa-838121.pdfCVE reference
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.
Operation on a Resource after Expiration or Release
Operation on a Resource after Expiration or Release represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.