What is CVE-2021-21985?

CVE-2021-21985 is VMware vCenter Server Improper Input Validation Vulnerability. The supplied enrichment data classifies it as SSRF mapped to CWE-918 Server-Side Request Forgery (SSRF); CWE-20 Improper Input Validation; CWE-470 CWE-470.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Yes: CISA KEV signal present. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

Yes. The supplied enrichment data lists CVE-2021-21985 in CISA KEV with required action: Apply updates per vendor instructions.. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

70 public PoC repositories reported; 2 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS, cloud metadata access logs, egress proxy logs where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2021-21985 using CVSS 9.8, EPSS 100%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

Publicly linked actor or ransomware signals in the supplied enrichment data: Ransomware use: Known. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Treat as emergency remediation because CISA KEV status is present. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

CISA KEVRansomwarecriticalSSRFpublic exploit

CVE-2021-21985

CVE-2021-21985 — VMware vCenter Server Improper Input Validation Vulnerability

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.

Published May 26, 2021Updated Jun 17, 2026Sources: NVD, VMware (CNA), CISA, FIRST EPSS, GitHub, GitHub Security Advisory

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Confirmed

CISA KEV, listed Nov 3, 2021

EPSS

100%

top of FIRST's scoreset

Affects

VMware

VMware vCenter Server and VMware Cloud Foundation

CVSS base

9.8

critical · 2 sources

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

Active

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade VMware vCenter Server and VMware Cloud Foundation to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

CISA required action

Apply updates per vendor instructions.

Federal deadline Nov 17, 2021 — passed 1,744 days ago

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Treat as emergency remediation because CISA KEV status is present.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
VMware	VMware vCenter Server and VMware Cloud Foundation	VMware vCenter Server (7.x before 7.0 U2b, 6.7 before 6.7 U3n, 6.5 before 6.5 U3p) and VMware Cloud Foundation (4.x before 4.2.1, 3.x before 3.10.2.1)	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Availability

High

Confidentiality

High

Integrity

High

Scope

Unchanged

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
9.8	CVSS 3.1	critical	3.9	5.9	NVD, CNA, GHSA
10	CVSS 2.0	high	10	10	NVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Weakness & attack patterns

CWE-918Server-Side Request Forgery (SSRF)
CWE-20Improper Input Validation
CWE-470

Inferred from the weakness class — not observed against this CVE.

CAPEC-664 · Server Side Request Forgery

T1562.003Impair Defenses: Impair Command History Logging
T1574.006Hijack Execution Flow: Dynamic Linker Hijacking
T1574.007Hijack Execution Flow: Path Interception by PATH Environment Variable

CISA KEV details

CISA lists a CVE here once it has evidence of exploitation against real targets.

CISAThat month →

Listed

Nov 3, 2021

Federal deadline

Nov 17, 2021

passed 1,744 days ago

Ransomware use

Known

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a date to argue against.

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

2 of the 5 sampled are weaponized

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable VMware vCenter Server and VMware Cloud Foundation.
Monitor for scanner or exploit-pattern traffic after 70 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPScloud metadata access logsegress proxy logs

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 9.8 (AV:N)
Jun 17, 2026 · NVD
2022
Added · GHSA-rg6m-2r9v-c5fj published (critical)
May 24, 2022 · GitHub Security Advisory
2021
Added to CISA KEV catalog
Nov 3, 2021 · CISA
Initial · CVE published
May 26, 2021 · NVD

References

6 on the record

packetstormsecurity.com/files/162812/VMware-Security-Advisory-2021-0010.html
Third Party Advisory, VDB Entry
packetstormsecurity.com/files/163487/VMware-vCenter-Server-Virtual-SAN-Health-Check-Remote-Code-Execution.html
Exploit, Third Party Advisory, VDB Entry
www.vmware.com/security/advisories/VMSA-2021-0010.html
Vendor Advisory
www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21985
US Government Resource
nvd.nist.gov/vuln/detail/CVE-2021-21985
NVD, Vendor Advisory
github.com/advisories/GHSA-rg6m-2r9v-c5fj
Exploit, Third Party Advisory

Elsewhere on this site

VMwareevery CVE for this vendor
November 2021what else CISA listed
SSRFsame class
CWE-918other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2021-21985 is VMware vCenter Server Improper Input Validation Vulnerability, a critical vulnerability affecting VMware vCenter Server and VMware Cloud Foundation from VMware. The current evidence lists it in CISA KEV, and the exploit status is: Yes: CISA KEV signal present. Public exploit evidence is: 70 public PoC repositories reported; 2 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 9.8 describes technical severity, while EPSS 100% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.