Security readout for executives and security teams
Plain-English summary
This issue can temporarily knock affected Phoenix Contact FL COMSERVER UNI devices offline by triggering an invalid Modbus exception response. It is availability-only, but in industrial environments a device outage can disrupt monitoring or communications. The source bundle does not show active exploitation.
Executive priority
Treat this as a high-priority availability risk where affected devices support production, safety-adjacent monitoring, or critical operations. Prioritize inventory and firmware validation before emergency action, because evidence of active exploitation is not provided.
Technical view
CVE-2021-21002 affects Phoenix Contact FL COMSERVER UNI versions before 2.40. CVSS 3.1 is 7.5, network-accessible, low complexity, no privileges, no user interaction, with high availability impact only. The mapped weakness is CWE-772, indicating resource handling or release problems.
Likely exposure
Exposure is limited to organizations using the listed FL COMSERVER UNI 232/422/485 or UNI 232/422/485-T products on vulnerable firmware below 2.40, especially where Modbus-related network access is reachable from less-trusted networks.
Exploitation context
The provided sources do not identify public exploitation, and the CVE is not listed as KEV in the bundle. The CVSS vector still indicates a remotely reachable, unauthenticated denial-of-service condition with low attack complexity.
Researcher notes
The public bundle gives only a concise vulnerability description. It identifies invalid Modbus exception response handling and temporary denial of service, but does not provide deeper protocol details, exploit status, or full remediation text beyond the version boundary.
Mitigation direction
- Identify affected FL COMSERVER UNI models in operational networks.
- Check Phoenix Contact guidance for firmware 2.40 or later.
- Restrict Modbus and management access to trusted network zones.
- Monitor affected devices for unexpected resets or communication outages.
- Plan maintenance windows before updating industrial devices.
Validation and detection
- Inventory device model numbers against the affected Phoenix Contact list.
- Confirm each device firmware version is below, at, or above 2.40.
- Review firewall rules for network reachability to affected devices.
- Check operational logs for temporary denial-of-service symptoms.
- Document compensating controls for devices that cannot be updated.
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-772: 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-2021-21002 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
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:H3.93.6Primary 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
Source materials
- CVE List V5 sourceCVE List V5
- https://cert.vde.com/en-us/advisories/vde-2021-022CVE 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.
Missing Release of Resource after Effective Lifetime
Missing Release of Resource after Effective Lifetime represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.