How severe is CVE-2021-21973?

CVE-2021-21973 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which products are affected by CVE-2021-21973?

CVE-2021-21973 affects the following products: vmware cloud foundation, vmware vcenter server.

How do I patch CVE-2021-21973?

Apply the vmware cloud foundation security patch or hotfix for CVE-2021-21973 on the affected version, following the vendor advisory for your exact build.

How do I detect CVE-2021-21973 across my infrastructure?

Inventory every vmware cloud foundation deployment and check each version against the affected-products list above.

How do I mitigate CVE-2021-21973 if there is no patch (or I can't update yet)?

Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

Is CVE-2021-21973 actively exploited in the wild?

Yes. There are 4 known exploit references for CVE-2021-21973, including 4 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-21973?

CVE-2021-21973 has an EPSS (Exploit Prediction Scoring System) score of 88.0%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2021-21973 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-21973 (VMware vCenter Server and Cloud Foundation Server Side Request Forgery (SSRF) Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2022-03-07. CISA required all US federal civilian agencies to remediate this vulnerability by 2022-03-21. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-21973?

CVE-2021-21973 is classified as Server-Side Request Forgery (SSRF) (CWE-918). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Which products and versions are affected by CVE-2021-21973?

CVE-2021-21973 affects vmware cloud foundation; vmware vcenter server (3 versions, e.g. 6.5, 6.7, 7.0). Check the affected-products list on this page against your deployed version to confirm exposure.

Is there exploit tooling available for CVE-2021-21973?

A Nuclei detection template exists for CVE-2021-21973, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-21973 published, and has it been updated?

CVE-2021-21973 was published on February 24, 2021 and was last updated on June 17, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🛡️

CISA KEV · ACTIVELY EXPLOITED

MEDIUM severity

CVE-2021-21973 — Cloud Foundation

MEDIUM

CVE-2021-21973 is a medium-severity (CVSS 5.3) Server-Side Request Forgery (SSRF) vulnerability in vmware cloud foundation. It is in CISA's Known Exploited Vulnerabilities catalog (added 2022-03-07) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

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…

Published

Feb 24, 2021

Updated

Jun 17, 2026

Affected

2 products

Patched

See advisory

Exploits

4 known

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2022-03-07. Federal agencies were required to remediate by 2022-03-21.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-21973.

EPSS Exploitation Probability

via FIRST.org ↗

88.0%probability of exploitation in next 30 days

Very High Risk+0.37%

Lower risk than most CVEs100th percentile — riskier than 100% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-21973 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the 50–90% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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).

Affected Products

2 products · 43 configurations

Application

cloud foundationvmware

≥ 4.0 && < 4.2

range

Application

vcenter servervmware

3 versions

6.56.77.0

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery…

github.comGithubMar 2021

The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery…

github.comAPIMar 2021

The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery…

cisa.govAPIMar 2022

The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery…

cisa.govCISAMar 2022

Detection & mitigation playbook

Vendor / appliance

Detect
Inventory every vmware cloud foundation deployment and check each version against the affected-products list above.
Fix
Apply the vmware cloud foundation security patch or hotfix for CVE-2021-21973 on the affected version, following the vendor advisory for your exact build.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.

How to detect CVE-2021-21973

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2021-21973 -u https://target

Template: VMware vSphere - Server-Side Request Forgery
Severity: medium
Impact: Successful exploitation of this vulnerability could allow an attacker to send arbitrary requests from the vulnerable server, potentially leading to unauthorized access, data leakage, or further attacks.
Remediation: Apply the necessary security patches or updates provided by VMware to mitigate this vulnerability.

Template by ProjectDiscovery nuclei-templates (pdteam), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

O3 Security · Runtime Protection

Is CVE-2021-21973 being exploited in your environment?

Detect and block the exploit chain at execution, on systems you cannot patch yet.

Protect my workloads How runtime protection works

CVSS Score

5.3/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Raw vector

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

CWE Classification

CWE-918Server-Side Request Forgery (SSRF)

Weaponization

Timeline

Disclosed

Feb 24, 2021

First exploit

Mar 16, 2021

KEV added

Mar 7, 2022

Last updated

Jun 17, 2026

Identifiers

CVE-2021-21973

References

Advisoryvmware.com Advisoryvmware.com Webcisa.gov

Related vulnerabilities

This CVE is medium severity; 8 of 8 other CVEs with CWE-918 are rated as high or higher (top: critical).

CVE-2026-115886CVE-2026-62197CVE-2026-113671CVE-2026-111761CVE-2026-77524GHSA-p3pr-8f3m-4qp8CVE-2026-107394CVE-2026-60091Browse all CWE-918

Provenance

Sources

OSV.devNVDCISA KEVFIRST.org (EPSS)

Last verifiedJun 17, 2026

CVE-2021-21973 — Cloud Foundation

Exploitation Status

Actively exploited in the wild

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Description

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

How to detect CVE-2021-21973

Frequently Asked Questions

Is CVE-2021-21973 being exploited in your environment?