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?

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

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. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.

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

Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.

How does O3 Security protect against CVE-2021-21973?

O3 detects and blocks CVE-2021-21973 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

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·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

Jun 17, 2026

Affected

0 pkgs

Patched

None yet

Exploits

4 known

EPSS Exploitation Probability

via FIRST.org ↗

88.0%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

Detection & mitigation playbook

Vendor / appliance

Detect
Inventory every vmware cloud foundation deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for exploitation at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
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
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2021-21973 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.

Tailored to CVE-2021-21973. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

O3 Security · Runtime Protection

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

O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-21973 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.

Protect my workloads How runtime protection works

CVE-2021-21973

EPSS Exploitation Probability

Description

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

How O3 protects you

Frequently Asked Questions

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