Security readout for executives and security teams
Plain-English summary
Siemens APOGEE and TALON building automation controllers contain a web server buffer overflow. A remote unauthenticated attacker could execute code as root on an affected device. This is critical for facilities and OT environments because compromised controllers may affect building systems and provide a foothold inside operational networks.
Executive priority
Prioritize this as critical where affected controllers are reachable beyond tightly controlled OT networks. The business risk is high because successful compromise gives root-level control of building automation devices, but the supplied evidence does not confirm active exploitation.
Technical view
The device web server lacks proper bounds checking while parsing the HTTP Host parameter, creating a CWE-120 buffer overflow. CVSS 3.1 is 9.8 with network attack vector, low complexity, no privileges, and no user interaction. Impact is high for confidentiality, integrity, and availability.
Likely exposure
Exposure is limited to environments running the listed Siemens APOGEE or TALON controller versions with reachable web services. Internet-facing or broadly reachable OT/building automation networks are highest risk. The source bundle does not provide asset prevalence or exposure counts.
Exploitation context
The source bundle supports remote unauthenticated arbitrary code execution with root privileges. It does not cite active exploitation, public exploit availability, or CISA KEV listing; KEV is marked false. Treat exploitation as plausible but not confirmed from the supplied evidence.
Researcher notes
Focus validation on asset identity, firmware branch, web service reachability, and segmentation boundaries. Avoid assuming a universal patch path: the bundle names V3.5.3 thresholds for BACnet products but does not provide complete remediation details for every listed P2 Ethernet product.
Mitigation direction
- Identify affected APOGEE and TALON controller models and firmware versions.
- Review Siemens SSA-944498 for product-specific updates and mitigations.
- For BACnet-listed products, prioritize moving versions below V3.5.3 to vendor-supported fixed guidance.
- Restrict web access to trusted management networks only.
- Remove direct internet exposure for affected controller web interfaces.
- Monitor vendor advisories for P2 Ethernet versions where fixed versions are not named here.
Validation and detection
- Inventory Siemens APOGEE MBC, MEC, PXC Compact, PXC Modular, and TALON TC controllers.
- Confirm whether each device version falls within the affected ranges.
- Check whether the device web server is reachable from user, corporate, or internet-facing networks.
- Verify remediation status against Siemens SSA-944498.
- Review logs or monitoring for unusual access to controller web services.
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-120: 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 lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2021-27391 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
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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.
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:H/I:H/A:H3.95.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://cert-portal.siemens.com/productcert/pdf/ssa-944498.pdfCVE reference · 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.
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
Buffer Copy without Checking Size of Input ('Classic Buffer Overflow') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.