ESXi
CVE-2021-21994
CRITICAL
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A07:2025 - Authentication Failures
ASVS 5.0
V6 - Authentication Authentication mechanism validation
MITRE ATT&CK
2 techniques across 2 tactics: Defense Evasion, Initial Access The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 9.8 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could bypass authentication mechanisms to gain unauthorized access by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAI
SFCB (Small Footprint CIM Broker) as used in ESXi has an authentication bypass vulnerability. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Implement multi-factor authentication, enforce strong password policies, use proven authentication frameworks.
Affects your stack
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Technical ContextAI · show details
This vulnerability is classified as Improper Authentication (CWE-287), which allows attackers to bypass authentication mechanisms to gain unauthorized access. SFCB (Small Footprint CIM Broker) as used in ESXi has an authentication bypass vulnerability. A malicious actor with network access to port 5989 on ESXi may exploit this issue to bypass SFCB authentication by sending a specially crafted request. Affected products include: Vmware Cloud Foundation, Vmware Esxi.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
SFCB (Small Footprint CIM Broker) as used in ESXi has an authentication bypass vulnerability. A malicious actor with network access to port 5989 on ESXi may exploit this issue to bypass SFCB authentication by sending a specially crafted request.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Affected Products (CPE)NVD
OpenSLP as used in VMware ESXi (7.0 before ESXi_7.0.1-0.0.16850804, 6.7 before ESXi670-202010401-SG, 6.5 before ESXi650-
VMware ESXi and Workstation contain a TOCTOU race condition leading to out-of-bounds write, allowing local administrator
Systems with microprocessors utilizing speculative execution and branch prediction may allow unauthorized disclosure of
VMware ESXi contains an arbitrary write vulnerability that allows privileged VMX process users to trigger kernel writes,
Untrusted search path vulnerability in the HGFS (aka Shared Folders) feature in VMware Tools 10.0.5 in VMware ESXi 5.0 t
VMware ESXi, Workstation, and Fusion contain an information disclosure vulnerability via HGFS out-of-bounds read, allowi
OpenSLP as used in ESXi and the Horizon DaaS appliances has a heap overwrite issue. Rated critical severity (CVSS 9.8),
In the add_match function in libbb/lineedit.c in BusyBox through 1.27.2, the tab autocomplete feature of the shell, used
VMware ESXi (ESXi 6.5 without patch ESXi650-201707101-SG), Workstation (12.x before 12.5.7) and Fusion (8.x before 8.5.8
The Service Location Protocol (SLP, RFC 2608) allows an unauthenticated, remote attacker to register arbitrary services.
The Virtual Machine Communication Interface (VMCI) implementation in vmci.sys in VMware Workstation 8.x before 8.0.5 and
VMware ESXi (6.5 before ESXi650-201710401-BG), Workstation (12.x before 12.5.8), and Fusion (8.x before 8.5.9) contain a
GitHub PoC
Exploit-DB