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 packages are affected by CVE-2021-21973?

Affected package information for CVE-2021-21973 is not yet fully mapped. Check the official advisory links for details.

How do I fix CVE-2021-21973?

No fixed version has been published for CVE-2021-21973 yet. Monitor the advisory for updates, apply mitigations recommended by the vendor, and use O3 Security to track when a fix becomes available in your stack.

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 90.4%, 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 October 30, 2025. 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·Added 2022-03-07 — agencies required to remediate by 2022-03-21

CVE-2021-21973

MEDIUM

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

Oct 30, 2025

Affected

0 pkgs

Patched

None yet

Exploits

4 known

EPSS Exploitation Probability

via FIRST.org ↗

90.4%probability of exploitation in next 30 days

Very High Risk100th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-21973 in your stack?

O3 detects CVE-2021-21973 across dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

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