CVE-2021-21972
CRITICALCVE-2021-21972 is a critical-severity (CVSS 9.8) Path Traversal vulnerability in vmware cloud foundation. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) and has been used in ransomware campaigns — treat it as actively exploited and patch now. O3 Security detects and blocks CVE-2021-21972 exploitation at runtime via eBPF exploit-chain detection and L7 egress monitoring, even on unpatched systems.
The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter Server plugin. A malicious actor with network access to port 443 may exploit this issue to execute…
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 — including use in ransomware campaigns. Federal agencies were required to remediate by 2021-11-17.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2021-21972.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2021-21972 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE sits: patch-first territory.
Where this sits among everything scored
Of 368,770 CVEs with a current EPSS score, this one falls in the ≥ 90% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Description
The vSphere Client (HTML5) contains a remote code execution vulnerability in a vCenter Server plugin. 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. 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).
Affected Products
cloud foundationvmwarevcenter servervmwareResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
VMware vCenter Server 7.0 - Remote Code Execution (RCE) (Unauthenticated)
by CHackA0101 · Jun 24, 2021
VMware vCenter Server 7.0 - Unauthenticated File Upload
by Photubias · Mar 1, 2021
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every vmware cloud foundation deployment and check each version against the affected-products list above. Because the exploit targets the running system rather than your application code, also watch for remote code execution at the network and runtime layer — O3 flags the exploit behaviour from runtime telemetry and egress traffic even before a vulnerable build is confirmed.
Fix
Apply the vmware cloud foundation security patch or hotfix for CVE-2021-21972 on the affected version, following the vendor advisory for your exact build.
Workarounds
Cut exposure now: restrict the management/admin interface to trusted networks, segment the device, and apply the vendor's recommended configuration mitigations and any WAF/IPS signature. O3's runtime protection blocks the exploit chain at execution, holding the line on unpatched or end-of-life systems until you can patch.
How O3 protects you
O3 detects and blocks CVE-2021-21972 exploitation at runtime: eBPF exploit-chain detection, plus L7 egress monitoring that catches the post-exploitation callback and severs the attacker's outbound channel.
Tailored to CVE-2021-21972. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21972 being exploited in your environment?
O3's eBPF runtime sensors and L7 egress monitoring detect and block the CVE-2021-21972 exploit chain at execution — protecting unpatched and end-of-life systems until the vendor patch is applied.