Security readout for executives and security teams
Plain-English summary
CVE-2021-40365 is a denial-of-service issue in several Siemens SIMATIC controllers. A remote, unauthenticated attacker could send specially crafted traffic to TCP port 102 and make an affected device unavailable. The business risk is operational disruption, not data theft or command execution based on the provided sources.
Executive priority
Prioritize as a high OT availability risk where affected controllers support production or safety-critical processes. Internet or enterprise-network exposure should trigger urgent containment and patch planning. Isolated lab or non-critical systems can follow normal maintenance windows.
Technical view
Affected Siemens SIMATIC devices mishandle specially crafted packets sent to port 102/tcp. The CVSS 3.1 score is 7.5 high, with network attack vector, low complexity, no privileges, no user interaction, and high availability impact only. CWE-20 indicates improper input validation.
Likely exposure
Exposure is most likely in OT environments using listed Siemens SIMATIC S7-1200, S7-1500, Drive Controller, or ET 200SP Open Controller models below the fixed version thresholds. Risk increases if TCP/102 is reachable beyond tightly controlled engineering or automation networks.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. CVSS marks exploit code maturity as proof-of-concept, but no exploit details are provided here. Treat this as credible denial-of-service risk for exposed OT assets.
Researcher notes
The provided evidence supports denial of service through malformed traffic to Siemens industrial controllers on TCP/102. It does not support confidentiality, integrity, code execution, or confirmed active exploitation claims. Affected-product evidence is partial in the bundle and should be cross-checked against Siemens SSA-382653.
Mitigation direction
- Upgrade affected Siemens devices to the fixed versions indicated by Siemens guidance.
- Review Siemens SSA-382653 for model-specific update and remediation instructions.
- Restrict TCP/102 access to authorized OT engineering and control systems only.
- Prioritize remediation for controllers supporting safety, production, or critical facility operations.
Validation and detection
- Inventory Siemens SIMATIC controllers and map exact model and firmware versions.
- Identify devices below V2.9.7, V21.9.7, or V4.6.0 as applicable.
- Check whether TCP/102 is reachable from untrusted or non-OT network zones.
- Confirm maintenance records show vendor-approved firmware updates or documented compensating controls.
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-20: 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-2021-40365 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-382653.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.
Improper Input Validation
Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.