VMware ESXi OpenSLP Use-After-Free Remote Code Execution Vulnerability (CVE-2020-3992) Analysis and Mitigation Guide
Executive & SecOps Summary
SECOPS ASSESSMENTVMware ESXi 7.0 (prior to ESXi_7.0.1-0.0.16850804), 6.7 (prior to ESXi670-202010401-SG), and 6.5 (prior to ESXi650-202010401-SG)
A malicious actor with access to port 427 on the management network can trigger a Use-After-Free in the OpenSLP service, leading to unauthenticated Remote Code Execution (RCE)
Apply the official VMware security patches immediately, or disable the OpenSLP service on ESXi hosts as a temporary workaround
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Apply the official security patches provided by VMware. You can upgrade the ESXi host directly via the command line interface as follows:
# Place the ESXi host into maintenance mode
esxcli system maintenanceMode set --enable true
# Enable HTTP outbound traffic in the firewall
esxcli network firewall ruleset set -e true -r httpClient
# Update the ESXi software profile to the patched version (Example for ESXi 6.7)
esxcli software profile update -p ESXi-6.7.0-20201004001-standard -d https://hostupdate.vmware.com/software/VUM/PRODUCTION/main/vmw-depot-index.xml
# Reboot the host and disable maintenance mode
reboot
esxcli system maintenanceMode set --enable false2. Temporary Workaround & Hardening Configuration
If patching cannot be performed immediately, disable the OpenSLP service to eliminate the attack vector.
# Stop the OpenSLP service
/etc/init.d/slpd stop
# Disable the OpenSLP service from starting on boot
esxcli system service set -s slpd -e false3. Log Audit & IoC Verification Commands
Verify whether the OpenSLP service is running and if port 427 is actively listening on the ESXi host.
# Check the status of the slpd service (vulnerable if 'running')
/etc/init.d/slpd status
# Check if port 427 is listening on network interfaces
localcli network ip connection list | grep 427Detect Container Escape & Privilege Escalation Across Your Kubernetes Fleet
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2020-3992) is a Use-After-Free (UAF) memory corruption flaw within the OpenSLP component used in VMware ESXi. The root cause lies in the improper handling of memory pointers during the processing of Service Location Protocol (SLP) network packets (CWE-416). When the OpenSLP service fails to properly invalidate or clear pointers to memory blocks that have already been freed, it allows subsequent operations to reference freed memory, leading to arbitrary code execution.
2. Exploitation Mechanics & Attack Scenario
An attacker residing in the management network with network line-of-sight to TCP/UDP port 427 on an ESXi host can initiate the attack. By sending crafted SLP messages, the attacker triggers the deallocation of a specific object in memory and subsequently reclaims that memory space with attacker-controlled data. When the OpenSLP service attempts to reuse the freed pointer, control flow is hijacked, executing the attacker's payload with administrative privileges on the hypervisor.
3. Infrastructure & Business Impact
Because VMware ESXi serves as the foundational hypervisor for enterprise virtualization, successful exploitation of this vulnerability poses an existential threat to the entire infrastructure. An attacker gaining RCE on the ESXi host can compromise all hosted virtual machines, exfiltrate sensitive data, deploy ransomware, or cause complete operational downtime. This vulnerability is actively exploited in the wild, as confirmed by its inclusion in the CISA KEV catalog and its high EPSS score of over 0.83.
Official Vendor Advisories & References
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 ESXi650-202010401-SG) has a use-after-free issue. A malicious actor residing in the management network who has access to port 427 on an ESXi machine may be able to trigger a use-after-free in the OpenSLP service resulting in remote code execution.
Frequently Asked SecOps Questions (CVE-2020-3992)
FAQQ1. How critical is CVE-2020-3992 and is it actively exploited in the wild?
CVE-2020-3992 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 83.0%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2020-3992?
Primary impacted vendors include vmware across esxi. Scope summary: VMware ESXi 7.0 (before ESXi_7.0.1-0.0.16850804), ESXi 6.7 (before ESXi670-202010401-SG), ESXi 6.5 (before ESXi650-202010401-SG)
Q3. What temporary mitigations or workarounds exist for CVE-2020-3992 before patching?
[Mitigation] Apply the official VMware security patches immediately, or disable the OpenSLP service on ESXi hosts as a temporary workaround Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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