Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2021-21973

VMware vCenter Server Server-Side Request Forgery

VMware vCenter Server · 7.x before 7.0 U1c

Watch CVE-2021-21973 Browse KEV feed
Severity
CVSS 5.3 · Medium
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
88.0%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-21973 is an unauthenticated vulnerability affecting VMware vCenter Server, VMware Cloud Foundation. The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery) vulnerability due to improper...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV.

Who is affected?

VMware vCenter Server 7.x before 7.0 u1c.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

VMware vCenter Server Server-Side Request Forgery

The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery) vulnerability due to improper validation of URLs in a vCenter Server plugin. A malicious actor with network access to port 443 may exploit this issue by sending a POST request to vCenter Server plugin leading to information disclosure.

This affects: VMware vCenter Server (7.x before 7.0 U1c, 6.7 before 6.7 U3l and 6.5 before 6.5 U3n) and VMware Cloud Foundation (4.x before 4.2 and 3.x before 3.10.1.2).

n/a Affected
VMware vCenter Server
7.x before 7.0 U1c 6.7 before 6.7 U3l 6.5 before 6.5 U3n
n/a Affected
VMware Cloud Foundation
4.x before 4.2 3.x before 3.10.1.2
Published
24 Feb 2021
Exploitation Reported
07 Mar 2022
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

cisa nuclei_scanner

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 07 Mar 2022

A trusted third party reported exploitation.

Proof of concept available

Nuclei Templates

Recorded 12 Jun 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

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Source Added
CISA First 2022-03-07 00:00 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-21973.yaml 25 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

5.3 Medium

Potential damage if exploited. Separate from whether attackers are using it.

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

EPSS

88.0%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Server-Side Request Forgery (SSRF) CWE-918

All CVSS Scores

CVSS v3.1 5.3 Medium

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

CVSS v2.0 5.0 Medium

AV:N/AC:L/Au:N/C:P/I:N/A:N

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

VMware vSphere - Server-Side Request Forgery

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 14:20 UTC

    Public PoC available

    Public proof-of-concept code published

  2. 00:00 UTC

    Nuclei template available

    Scanner coverage available

  3. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  4. 16:42 UTC

    CVE published

    Vulnerability disclosed publicly

  5. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-21973

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2021-21973",
  "confidence": "Confirmed",
  "cvss_score": 5.3,
  "cvss_estimated": false,
  "epss_score": 0.88012,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}