Security readout for executives and security teams
Plain-English summary
This Siemens issue affects DNS parsing in selected building automation, industrial connectivity, and Nucleus embedded products. A malformed DNS response can make affected software read beyond allocated memory, potentially disrupting device availability. The attacker needs a privileged network position, so urgency depends heavily on whether these devices can receive attacker-influenced DNS traffic.
Executive priority
Handle as a moderate operational resilience issue. It is not presented as actively exploited, but affected building automation or industrial systems can be business-critical and may have limited maintenance windows. Prioritize internet-adjacent or weakly segmented deployments first.
Technical view
The flaw is improper validation of DNS decompression pointer offsets, mapped to CWE-788. Parsing malformed DNS responses can trigger an out-of-bounds read. CVSS 3.1 is 6.5 with network attack vector, high attack complexity, no privileges or user interaction, low confidentiality impact, and high availability impact.
Likely exposure
Exposure is most likely in environments running listed Siemens APOGEE, TALON, SIMOTICS CONNECT 400, Nucleus ReadyStart, Nucleus NET, or Nucleus Source Code versions with affected DNS modules. Building automation and embedded deployments may be harder to inventory, increasing operational risk.
Exploitation context
The provided sources do not show CISA KEV listing or confirmed active exploitation. The CVE states exploitation requires a privileged network position and malformed DNS responses. Treat this primarily as a denial-of-service risk against reachable affected devices.
Researcher notes
Evidence supports denial of service from malformed DNS response parsing, with possible low confidentiality impact per CVSS. The source bundle does not provide exploit details, proof-of-concept status, or full per-product remediation text beyond affected version thresholds and Siemens advisory links.
Mitigation direction
- Upgrade affected products to the fixed versions named in Siemens guidance where available.
- For Nucleus NET and source-code users, check Siemens advisories for product-specific remediation guidance.
- Prioritize remediation for devices on networks where DNS responses could be attacker-influenced.
- Reduce untrusted network paths to affected devices until vendor guidance is applied.
- Track Siemens advisories SSA-705111, SSA-669158, and SSA-180579 for exact update details.
Validation and detection
- Inventory Siemens product models and firmware versions against the affected version ranges.
- Identify any embedded use of Nucleus DNS modules in source-code deployments.
- Confirm whether affected devices perform DNS lookups across untrusted or shared network paths.
- Verify upgrades meet or exceed the fixed versions listed in the CVE record.
- Document residual systems where no product-specific fix is named in the provided sources.
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-788: 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-2020-27738 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
- Medium
- CVSS
- 6.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/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:H/PR:N/UI:N/S:U/C:L/I:N/A:H/E:P/RL:O/RC:C2.24.2Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.5MediumVector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H/E:P/RL:O/RC:C
Source materials
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.
Access of Memory Location After End of Buffer
Access of Memory Location After End of Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.