Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2021-21985 is a critical-severity SSRF (CWE-918) vulnerability in Vmware Vcenter Server. Its CVSS base score is 9.8 (Critical).
Operationally, exploitation aligns with the MITRE ATT&CK technique Data Obfuscation (T1001); ranked in the top 0.0% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
The vulnerability CVE-2021-21985 is a remote code execution flaw in the vSphere Client (HTML5) caused by insufficient input validation in the Virtual SAN Health Check plug-in. This component is enabled by default in vCenter Server, and the weakness is tracked under CWEs 918, 20, and 470 with a CVSS 3.1 score of 9.8.
An unauthenticated attacker with network access to TCP port 443 can send crafted requests that result in arbitrary command execution with unrestricted privileges on the operating system hosting vCenter Server.
Public advisories and exploit references for the issue have been published by VMware and archived on Packet Storm at the listed URLs. No additional details on patch availability, exploitation in the wild, or other context are provided in the source data.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2021-9156
Vulnerability Data
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…
more
may exploit this issue to execute commands with unrestricted privileges on the underlying operating system that hosts vCenter Server.
- CWE(s)
- KEV Date Added
- 03 November 2021
Related Threats
Threat-Actor AttributionAI
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Directly implements checks on information inputs to reject invalid data before processing.
Penetration testing attempts server-side requests to internal resources, identifying SSRF weaknesses for remediation.
Security testing and developer training directly verify and enforce proper input validation, reducing exploitability of injection and malformed-data weaknesses.
Security testing and evaluation at multiple SDLC stages directly detects missing or flawed input validation, with the required remediation process ensuring fixes are applied.
Externally controlled class or code selection can be resolved and invoked inside the chamber, surfacing unsafe reflection without system impact.
Outbound connections to external resources can be monitored and limited at the boundary, reducing SSRF impact.
Detects server-side request forgery through monitoring of unexpected outbound connections.
Spam protection mechanisms perform filtering and detection on inbound/outbound messages, directly compensating for missing or weak input validation of unsolicited content.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Runtime monitoring of web applications and services can detect anomalous outbound requests indicative of SSRF.
Vulnerability identification processes can discover and record SSRF flaws in web applications.
Network segmentation and egress controls can limit the damage from successful SSRF requests.
Preventing execution of unauthorized code can block exploitation of unsafe reflection at runtime.
Secure development practices directly include input validation and destination allow-listing that prevent SSRF.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Hardening callouts derived
DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.
- No fine-grained STIG row for CWE-20, a class-level weakness, and none of its children carries one either.