CVE-2021-21985: VMware vCenter Server Improper Input Validation Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on , 161 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 100%
EPSS score, percentile 100 of all scored records
- How severe?
- 9.8 Critical
CVSS v3.1 base score, from CISA's enrichment of the record
- What should I do?
CISA deadline . Apply updates per vendor instructions.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- VMware vCenter Server (7.x before 7.0 U2b, 6.7 before 6.7 U3n, 6.5 before 6.5 U…
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
What to do
Required action, set by CISA
Apply updates per vendor instructions.
CISA due date for this action: .
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | VMware vCenter Server (7.x before 7.0 U2b, 6.7 before 6.7 U3n, 6.5 before 6.5 U… |
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
About this vulnerability
VMware vSphere Client contains an improper input validation vulnerability in the Virtual SAN Health Check plug-in, which is enabled by default in vCenter Server, which allows for remote code execution.
Summary: CISA's KEV catalog, as of .
- CISA added CVE-2021-21985 to its Known Exploited Vulnerabilities (KEV) catalog on 3 Nov 2021.
- CISA marks it as known to be used in ransomware campaigns.
- The due date CISA sets for the required action is 17 Nov 2021.
- The CVE record was published on 26 May 2021, 161 days before it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), taken from CISA's enrichment of the record.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 100% (percentile 100), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable yes, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of ; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of ; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of . About the data.
Description
The vSphere Client (HTML5) contains a remote code execution vulnerability due to lack of input validation in the Virtual SAN Health Check plug-in which is enabled by default in vCenter Server. A malicious actor with network access to port 443 may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of . About the data.
Weakness
- CWE-20: Improper Input Validation
- CWE-470: Use of Externally-Controlled Input to Select Classes or Code ('Unsafe Reflection')
- CWE-918: Server-Side Request Forgery (SSRF)
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| Added to CISA KEV | |
| CISA due date for the required action | |
| CVE record last updated |
References
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