Security readout for executives and security teams
Plain-English summary
Certain Phoenix Contact FL SWITCH SMCS and FL NAT SMN industrial switch products can have their web, SNMP, and ping services disrupted by fragmented TCP packets. The switching function is reported as unaffected, so this is primarily a management and monitoring availability issue rather than a traffic-forwarding outage.
Executive priority
Treat this as a moderate operational resilience issue. It is unlikely to stop switching based on current sources, but it can impair visibility and administration of affected industrial network devices.
Technical view
CVE-2021-21003 is a network-reachable, unauthenticated denial-of-service issue in listed Phoenix Contact models. The CVSS 3.1 score is 5.3. Fragmented TCP packets may cause denial of service for Web, SNMP, and ICMP-Echo services. The record maps the weakness to CWE-404 and states switching functionality is not affected.
Likely exposure
Exposure is most relevant where affected device management or monitoring services are reachable from untrusted networks, shared operational networks, or poorly segmented environments. Organizations using the listed Phoenix Contact product numbers should inventory devices before assuming exposure.
Exploitation context
The provided sources do not state active exploitation, and the CVE is not marked KEV. The described attack is network-based and does not require authentication, but the documented impact is limited availability loss for management and monitoring services.
Researcher notes
Key evidence is limited to the CVE description and VDE advisory reference. No fixed version, exploit status, or detailed vendor workaround is included in the source bundle. Validate exact model numbers before remediation planning.
Mitigation direction
- Check Phoenix Contact and VDE guidance for supported firmware, fixes, or vendor mitigations.
- Limit access to Web, SNMP, and ICMP-Echo services to trusted management networks.
- Segment affected industrial switches from untrusted or general-purpose network traffic.
- Monitor device management availability for unexpected Web, SNMP, or ICMP-Echo outages.
Validation and detection
- Inventory Phoenix Contact devices and match product numbers against the affected list.
- Confirm whether Web, SNMP, or ICMP-Echo services are reachable from untrusted networks.
- Review monitoring history for unexplained management-plane availability interruptions.
- Document whether operations depend on these services during incident response or maintenance.
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-404: 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-2021-21003 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
- 5.3 (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:L
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:L3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.3MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source materials
- CVE List V5 sourceCVE List V5
- https://cert.vde.com/en-us/advisories/vde-2021-023CVE reference · x_refsource_CONFIRM
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 Resource Shutdown or Release
Improper Resource Shutdown or Release represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.