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NVD / CVE Program· CNA CERTVDE

CVE-2021-21005: Race Condition Vulnerability in Phoenix Contact FL SWITCH SMCS series products

Noroxi assessment

Priority: Monitor (action score 30/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.67% (FIRST EPSS); higher than 52.3% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to the record, no fixed version is available yet.

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In Phoenix Contact FL SWITCH SMCS series products in multiple versions if an attacker sends a hand-crafted TCP-Packet with the Urgent-Flag set and the Urgent-Pointer set to 0, the network stack will crash. The device needs to be rebooted afterwards.

HighCVSS 7.5 · v3.1—No exploit No fix recorded
Published
Jun 25, 2021
Updated
Jun 16, 2026
EPSS
0.6% · 52th percentile

Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.6%

CNA vs NVD score

NVD
7.5
CNA · CERTVDE
7.5
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-21005

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
phoenixcontactfl switch smcs 16tx firmware
phoenixcontactfl switch smcs 16tx
phoenixcontactfl switch smcs 14tx\/2fx firmware
phoenixcontactfl switch smcs 14tx\/2fx
phoenixcontactfl switch smcs 14tx\/2fx-sm firmware
phoenixcontactfl switch smcs 14tx\/2fx-sm
phoenixcontactfl switch smcs 8gt firmware
phoenixcontactfl switch smcs 8gt
phoenixcontactfl switch smcs 6gt\/2sfp firmware
phoenixcontactfl switch smcs 6gt\/2sfp
phoenixcontactfl switch smcs 8tx-pn firmware
phoenixcontactfl switch smcs 8tx-pn

and 18 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • phoenixcontact fl nat smn 8tx firmwareup to 4.63 inclusive
  • phoenixcontact fl nat smn 8tx-m firmwareup to 4.63 inclusive
  • phoenixcontact fl switch smcs 14tx/2fx firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 14tx/2fx-sm firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 16tx firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 4tx-pn firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 6gt/2sfp firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 6tx/2sfp firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 8gt firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 8tx firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smcs 8tx-pn firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smn 6tx/2fx firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smn 6tx/2fx sm firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smn 6tx/2pof-pn firmwareup to 4.70 inclusive
  • phoenixcontact fl switch smn 8tx-pn firmwareup to 4.70 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (CERTVDE). Independent of NVD's CPE analysis and usually ahead of it.

  • Phoenix Contact FL NAT

    • SMN 8TX (2989365) and later · up to and including 4.63affected
    • SMN 8TX-M (2702443) and later · up to and including 4.63affected

  • Phoenix Contact FL SWITCH

    • SMCS 16TX (2700996) and later · up to and including 4.70affected
    • SMCS 14TX/2FX (2700997) and later · up to and including 4.70affected
    • SMCS 14TX/2FX-SM (2701466) and later · up to and including 4.70affected
    • SMCS 8GT (2891123) and later · up to and including 4.70affected
    • SMCS 6GT/2SFP (2891479) and later · up to and including 4.70affected
    • SMCS 8TX-PN (2989103) and later · up to and including 4.70affected
    • SMCS 4TX-PN (2989093) and later · up to and including 4.70affected
    • SMCS 8TX (2989226) and later · up to and including 4.70affected
    • SMCS 6TX/2SFP (2989323) and later · up to and including 4.70affected
    • SMN 6TX/2POF-PN (2700290) and later · up to and including 4.70affected

Same product

phoenixcontact: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-21004Cross-site Scripting Vulnerability in Phoenix Contact FL SWITCH SMCS series products
    24Monitor
  • CVE-2021-21003Denial of Service Vulnerability in Phoenix Contact FL SWITCH SMCS series products
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-362 · Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records