CVE-2021-21973
MediumExploitedPublic exploitThe vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery) vulnerability due to improper validation of URLs in a vCenter Server plugin.
Published Mar 18, 2021 · Updated Oct 21, 2025
Key Facts
Patch immediately- CVE-2021-21973 is a medium-severity vulnerability (CVSS 5.3 v3.1) affecting Cloud Foundation (Vmware), Vcenter Server (Vmware).
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Feb 25, 2021. Public exploit code is available.
- EPSS estimates a 88% probability of exploitation in the next 30 days.
- Fixed versions are available, including Cloud Foundation 3.10.1.2.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS (30-day exploit likelihood)
88%
Higher than 99.7% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-21973 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
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).
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Mar 7, 2022 | Mar 21, 2022 | Not reported |
| Industry KEV feed | Feb 25, 2021 | Mar 21, 2022 | Not reported |
| CIRCL KEV | Mar 7, 2022 | Mar 21, 2022 | Not reported |
| ENISA EUVD | Mar 7, 2022 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
44 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Cloud FoundationVmware | >= 4.x before 4.2 | 3.10.1.2 |
| Vcenter ServerVmware | 6.5, 6.5-a, 6.5-b, 6.5-c, 6.5-d, 6.5-e, 6.5-f, 6.5-update1d | n/a |
Patched Releases
Cloud Foundation
3.10.1.2
Timeline
Added to Industry KEV feed
Feb 25, 2021
Publicly disclosed
Mar 18, 2021
Added to CISA KEV
Mar 7, 2022
Added to CIRCL KEV
Mar 7, 2022
Added to ENISA EUVD
Mar 7, 2022
Last updated
Oct 21, 2025
Weakness Type
- CWE-918 Server-Side Request Forgery (SSRF)
References
- advisoryhttps://borncity.com/win/2021/02/24/vmware-fixt-kritische-rce-schwachstelle-im-vsphere-html5-client/
- advisoryhttps://lifars.com/2021/03/vmware-warns-of-critical-remote-code-execution-vulnerability-in-vsphere-html5-client/
- advisoryhttps://us-cert.cisa.gov/ncas/current-activity/2021/02/24/vmware-releases-multiple-security-updates
- advisoryUSOM advisory
- advisoryUSOM advisory
FAQ
Common Questions.
The vSphere Client (HTML5) contains an SSRF (Server Side Request Forgery) vulnerability due to improper validation of URLs in a vCenter Server plugin.
Affected: Cloud Foundation (Vmware) versions >= 4.x before 4.2; Vcenter Server (Vmware) versions 6.5, 6.5-a, 6.5-b, 6.5-c, 6.5-d, 6.5-e, 6.5-f, 6.5-update1d. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Feb 25, 2021.
Yes. It was added on Mar 7, 2022 with a federal remediation due date of Mar 21, 2022.
Public exploit code is available.
Fixed versions are available, including Cloud Foundation 3.10.1.2.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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