Security readout for executives and security teams
Plain-English summary
Certain Phoenix Contact industrial switches can be forced into a crash by a malformed network packet, causing the device to require a reboot. The impact is availability loss, not data theft. For operational networks, this matters because switch downtime can interrupt monitoring, automation, or production connectivity.
Executive priority
Treat this as a high-priority OT availability risk if affected switches support production, safety-adjacent monitoring, or remote operations. Prioritize inventory confirmation, segmentation review, and vendor-guided remediation over emergency response unless crashes are observed.
Technical view
CVE-2021-21005 is a network-reachable race condition in listed Phoenix Contact FL SWITCH SMCS and FL NAT SMN products. The reported failure mode is network stack crash and required reboot. CVSS 3.1 is 7.5: low complexity, no privileges, no user interaction, availability impact only.
Likely exposure
Exposure is most relevant where affected Phoenix Contact switch models are reachable from untrusted or broadly accessible networks. Internet exposure is not stated in the sources. Internal exposure can still matter in flat OT networks, remote-access environments, or shared plant networks.
Exploitation context
The provided sources do not show active exploitation, and the CVE is not marked KEV. The vulnerability is still practical to trigger because the CVSS vector indicates network access, low attack complexity, and no authentication requirement.
Researcher notes
Evidence supports a denial-of-service condition, but the bundle does not provide firmware ranges, CPEs, patch identifiers, or confirmed exploit activity. The affected entries appear to be model identifiers. Validate exact product status against the vendor advisory before closing exposure.
Mitigation direction
- Identify affected Phoenix Contact model numbers in OT asset inventory.
- Check Phoenix Contact or VDE guidance for product-specific updates or mitigations.
- Restrict network access to affected devices from untrusted segments.
- Segment OT switching infrastructure from user and internet-facing networks.
- Prepare operational reboot procedures for unexpected device crashes.
- Monitor affected networks for unexpected switch reboots or availability loss.
Validation and detection
- Match deployed hardware against the affected model list in the CVE record.
- Confirm firmware and product guidance directly with Phoenix Contact or VDE.
- Review network diagrams for paths to affected switch management or data-plane interfaces.
- Check monitoring history for unexplained switch crashes or reboots.
- Avoid production packet-based crash testing unless vendor-approved.
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-362: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-21005 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-2021-023CVE 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.
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.