CVE-2021-21973
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).
- CVSS
- 5.3Mediumscored by CISA
- Exploited in the wild
- Yes, in CISA KEV since 7 Mar 2022CISA deadline for US federal agencies: 21 Mar 2022unvetted proof-of-concept code on github
- EPSS
- 88.0%chance of exploitation in the next 30 daystop 0.3% of scored CVEsFIRST score of 11 Nov 2026
- Fix
- Patch availablesee the advisories in the references
- Published
- 24 Feb 2021analysed here 12 Nov 2026
Do first. Apply updates per vendor instructions. (CISA's required action for this KEV entry)
Summary
Triage
The summary, impact and action text on this page are written by our AI analysis pipeline, or taken from the NVD description when a CVE was imported from NVD. They are not the vendor's wording: check them against the sources. A longer AI executive summary and technical analysis are generated for signed-in accounts on the Max plan.
Affected products
| Product | Affected versions | Vendor says fixed in |
|---|---|---|
| VMware Cloud Foundation | 4.x before 4.23.x before 3.10.1.2Vendor says fixed in: not stated | |
| VMware vCenter Server | 7.x before 7.0 U1c6.7 before 6.7 U3l6.5 before 6.5 U3nVendor says fixed in: not stated |
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
Products named in our analysis
- vmware:cloud_foundation
- vmware:vcenter_server
Fix and mitigation
WAF and other mitigations
Can a WAF block it? Partly. SSRF makes the server call a URL the attacker picks. A WAF can block well-known targets such as cloud metadata addresses, but not every internal host.
Also consider: egress filter · IMDSv2
Based on the weakness type only; no CVE-specific evidence yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Remediation steps (AI-written)
Step-by-step remediation is generated for accounts on the Max plan, for CVEs that match a technology in their stack. Add this technology to your stack to see the fix checklist.
Exploitation evidence
- CISA KEV catalog
- Listed since 7 Mar 2022.
- CISA due date
- 21 Mar 2022, the remediation deadline for US federal agencies
- CISA required action
- Apply updates per vendor instructions.
- Public exploit code
- Unvetted proof-of-concept code on GitHub: 1 GitHub proof of concept · 1 Nuclei template
- CISA SSVC
- exploitation active, automatable yes, technical impact partialAssessed by CISA 16 Feb 2024 (SSVC 2.0.3). Exploitation is none, poc (public proof of concept) or active.
Nuclei
- VMware vSphere - Server-Side Request Forgerydetection template, medium
GitHub proofs of concept
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
Timeline
- 24 Feb 2021Published
- 16 Mar 2021First proof-of-concept repository on GitHub (unvetted)19 days later
- 7 Mar 2022Added to CISA KEV (exploited in the wild)356 days (about 12 months) later
- 21 Mar 2022CISA remediation due date (US federal agencies)14 days later
- 16 Feb 2024CISA SSVC assessment: exploitation active698 days (about 2 years) later
- 21 Oct 2025CVE record last updated613 days (about 2 years) later
- 12 Nov 2026Analysed by vulneraibility.com387 days (about 1 year) later
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
| Metric | Value | What it means |
|---|---|---|
| Attack vector | NetworkReachable over the internet or any routable network. | Reachable over the internet or any routable network. |
| Attack complexity | LowRepeatable attack, no special conditions. | Repeatable attack, no special conditions. |
| Privileges required | NoneThe attacker needs no prior access. | The attacker needs no prior access. |
| User interaction | NoneNo victim action needed. | No victim action needed. |
| Scope | UnchangedImpact stays within the vulnerable component. | Impact stays within the vulnerable component. |
| Confidentiality | LowPartial data disclosure. | Partial data disclosure. |
| Integrity | NoneNo unauthorised modification. | No unauthorised modification. |
| Availability | NoneThe service stays up. | The service stays up. |
Common questions
Is CVE-2021-21973 being exploited?
Yes. CVE-2021-21973 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2021-21973?
CVE-2021-21973 is rated Medium with a CVSS score of 5.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-21973?
Yes. A fix has been recorded for CVE-2021-21973. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-21973 affect?
CVE-2021-21973 affects vmware:cloud_foundation, vmware:vcenter_server. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
References
2 references in the CVE record, grouped by the tags the record gives them.
Other links (2)
- vmware.com /security/advisories/VMSA-2021-0002.html
- cisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21973
Where the data on this page comes from
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- Nuclei templates: detection templates
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.
Similar CVEs
Get CVEs like this by email. Join the free digest: the CVEs we flag as major, all CVSS 8.0 or higher, in up to three emails a day (sent at 05:00, 11:00 and 15:00 UTC). Matching alerts to the products you run needs an account, and accounts are invite-only during the beta.