VMware ESXi 6.7 — openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide

📖 ~4 min read  •  Source: VMware advisory VMSA-2021-0002

Related CVEs: CVE-2020-3992 CVE-2021-21974

Fixed image profile / build: ESXi670-202102401-SG

Upstream summary: ESXi contains a heap-overflow vulnerability in the OpenSLP service (CVE-2020-3992 / CVE-2021-21974) that allows a malicious actor residing in the management network with port 427 access to execute remote code. This advisory is the root cause behind the ESXiArgs ransomware wave that swept un-patched ESXi 6.7 and 7.0 hosts.

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

On VMware ESXi 6.7 hosts where the openslp component ships an unpatched VIB, administrators see behaviour consistent with VMware advisory VMSA-2021-0002: hostd / vpxa restart loops, suspicious entries in /var/log/vmkernel.log and /var/log/hostd.log, and — for the CVEs listed above — exposure to guest-to-host escape, unauthenticated remote code execution, or privilege escalation on the hypervisor. Production impact ranges from a single host disconnect from vCenter to a full datacenter outage when openslp sits on the management or workload path.

Environment & Reproduction

Reproduction targets VMware ESXi 6.7. Confirm the running build, installed image profile and the affected component VIBs first — ESXi does not use a traditional package manager; everything is a VIB inside an image profile:

esxcli system version get
vmware -lv
esxcli software profile get
esxcli software vib list | grep -i openslp
esxcli software vib get -n openslp 2>/dev/null | head -40

Trigger the workflow that exposes openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide while tailing the hypervisor logs:

tail -200 /var/log/vmkernel.log
tail -200 /var/log/hostd.log
tail -200 /var/log/vpxa.log
tail -200 /var/log/syslog.log
# For an evidence bundle to attach to a Broadcom / VMware support case:
vm-support -w /vmfs/volumes/datastore1

Root Cause Analysis

Root cause is documented in VMware advisory VMSA-2021-0002. Broadcom / VMware shipped the corrective VIB inside a new ESXi image profile for VMware ESXi 6.7; hosts still running the pre-patch build retain the vulnerable openslp code path. Correlate the host history with logs to confirm:

esxcli software profile get
esxcli software vib list --rebooting-image 2>/dev/null | head
esxcli software vib get -n openslp 2>/dev/null | head -40
grep -i VMSA /var/log/esxupdate.log 2>/dev/null | tail
tail -200 /var/log/vmkernel.log

Quick Triage

Run these on VMware ESXi 6.7 (DCUI / SSH) to capture the current state of openslp and the host:

esxcli system version get                              # build & update level
esxcli software profile get                            # current image profile
esxcli software vib list | grep -i openslp
esxcli system maintenanceMode get
vim-cmd hostsvc/runtimeinfo | head -40                 # host runtime/config snapshot
esxcli network firewall ruleset list | head
esxcli vsan cluster get 2>/dev/null || echo 'vSAN not configured'
# DRS / cluster context (PowerCLI on a jump host):
# Connect-VIServer vc01 -User [email protected]
# Get-VMHost esx01 | Select Version, Build, ConnectionState

Step-by-Step Diagnosis

1. Confirm the openslp VIB and its origin.

   esxcli software vib list | grep -i openslp
   esxcli software vib get -n openslp 2>/dev/null | head -40

2. Tail the hypervisor logs while reproducing the issue.

   tail -F /var/log/vmkernel.log &
   tail -F /var/log/hostd.log &
   tail -F /var/log/vpxa.log &

3. Inspect the ESXi firewall posture (management network exposure for openslp / vpxa / hostd ports is the most common amplifier of these advisories).

   esxcli network firewall get
   esxcli network firewall ruleset list
   esxcli network firewall ruleset rule list | head -40

4. Check service state and cycle the affected daemon if it is hung.

   /etc/init.d/hostd status
   /etc/init.d/vpxa status
   /etc/init.d/hostd restart   # restarts management agent only — no VM impact
   /etc/init.d/vpxa restart

5. Confirm cluster context — DRS automation level, vMotion network and active maintenance-mode plans dictate the patch window.

   # PowerCLI on a jump host:
   Connect-VIServer vc01 -User [email protected]
   Get-Cluster Prod | Select Name, DrsEnabled, DrsAutomationLevel
   Get-VMHost esx01 | Get-View | Select Runtime | Format-List

6. Correlate findings with /var/log/esxupdate.log, /var/log/syslog.log and VMware advisory VMSA-2021-0002 to pin the build that introduced openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide.

Solution – Primary Fix

Apply the corrective ESXi image profile referenced by VMware advisory VMSA-2021-0002. The workflow is: evacuate workloads via DRS / vMotion, enter maintenance mode, pull the new profile (online from the VMware HCL or from an offline depot bundle), reboot, and exit maintenance mode.

# 1. (PowerCLI on jump host) Evacuate the host using DRS / vMotion:
Connect-VIServer vc01 -User [email protected]
Get-VM -Location esx01 | Move-VM -Destination esx02   # bulk vMotion
Set-VMHost esx01 -State Maintenance -Evacuate

# 2. On the ESXi host (SSH), enter maintenance mode from the CLI too:
esxcli system maintenanceMode set --enable=true

# 3a. Online patch direct from the VMware / Broadcom HCL depot:
esxcli software profile update 
  -p ESXi670-202102401-SG 
  -d https://hostupdate.vmware.com/software/VUM/PRODUCTION/main/vmw-depot-index.xml

# 3b. Or offline patch from a downloaded depot ZIP on a datastore:
esxcli software profile update 
  -d /vmfs/volumes/datastore1/VMware-ESXi-8.0U3-depot.zip 
  -p ESXi670-202102401-SG

# 4. Reboot to commit the new profile:
reboot

# 5. After reboot — verify and exit maintenance mode:
esxcli system version get
esxcli software profile get
esxcli system maintenanceMode set --enable=false

For a whole vSphere cluster, use vSphere Lifecycle Manager (vLCM) image-based remediation — this is the only supported workflow for ESXi 7 and 8 fleets and handles DRS evacuation, sequenced reboots and post-checks automatically:

Connect-VIServer vc01 -User [email protected]
Get-Cluster Prod | Test-LcmClusterCompliance
Set-Cluster Prod -Remediate -Confirm:$false
# Or via govc:
govc cluster.remediate -cluster=Prod

Solution – Alternative Approaches

If the primary image-profile update is not viable right now, choose from these:

• Apply only the relevant VIB(s) from an offline depot instead of the full profile (smaller blast radius, but you lose image-profile consistency):

  esxcli software sources vib list 
    -d /vmfs/volumes/datastore1/VMware-ESXi-8.0U3-depot.zip | head
  esxcli software vib update 
    -d /vmfs/volumes/datastore1/VMware-ESXi-8.0U3-depot.zip 
    -n openslp

• Apply the VMware-documented workaround / mitigation listed on the VMSA page (for OpenSLP-class advisories the documented workaround is to disable the SLP service entirely on the management network):

  esxcli network firewall ruleset set --enabled=false --ruleset-id=CIMSLP
  /etc/init.d/slpd stop
  chkconfig slpd off
  esxcli network firewall ruleset list | grep -i slp

• Roll forward only the affected hosts and version-pin the rest of the cluster until a maintenance window opens — set the vLCM baseline on a per-host basis instead of cluster-wide:

  Connect-VIServer vc01 -User [email protected]
  $img = Get-LcmImage -Name 'ESXi-8.0U3-stable'
  Set-VMHost esx01 -LcmImage $img -Remediate

• For an emergency rebuild, use the new image profile to stateless-boot the host via Auto Deploy rules; the next PXE boot picks up the patched profile automatically:

  Connect-VIServer vc01 -User [email protected]
  Get-DeployRule | Select Name, ItemList
  Copy-DeployRule -DeployRule prod-rule -ReplaceItem $newImage

• If a guest-to-host escape is feared and no patch window is available, suspend untrusted VMs and isolate the host on a dedicated VLAN until the VIB is applied:

  vim-cmd vmsvc/getallvms
  vim-cmd vmsvc/power.suspend <vmid>
  esxcli network vswitch standard portgroup set -p 'Quarantine' -v 999

Verification & Acceptance Criteria

All of these should pass after the patch window:

esxcli system version get                                # expected fixed build
esxcli software profile get                              # expected fixed profile
esxcli software vib list | grep -i openslp
esxcli system maintenanceMode get                        # should be 'Disabled'
tail -100 /var/log/vmkernel.log | grep -iE "error|fail" || echo OK
tail -100 /var/log/hostd.log    | grep -iE "error|fail" || echo OK
esxcli network firewall ruleset list | head
# Cluster-level compliance check via PowerCLI:
Get-Cluster Prod | Test-LcmClusterCompliance

The original reproduction for openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide must not trigger across two consecutive runs, and the VMware advisory VMSA-2021-0002 must report the host as remediated.

Rollback Plan

Capture state before any change:

esxcli system version get        > /tmp/esxi-pre.txt
esxcli software profile get      >> /tmp/esxi-pre.txt
esxcli software vib list         >> /tmp/esxi-pre.txt
# Persist host config — survives a reboot/reinstall:
vim-cmd hostsvc/firmware/backup_config
# (Download the resulting bundle from /scratch/downloads/<id>/configBundle-*.tgz)

To revert if the new profile is bad:

# 1. Enter maintenance mode and reboot — ESXi keeps the previous boot bank:
esxcli system maintenanceMode set --enable=true
reboot
# 2. At the boot loader, press <Shift+R> to roll back to the previous image
#    profile (ESXi keeps two boot banks for exactly this).
# 3. Or, from a working SSH session, force the previous profile back online:
esxcli software profile update -p <previous-profile> 
  -d /vmfs/volumes/datastore1/<previous-depot>.zip
reboot
esxcli system maintenanceMode set --enable=false

Prevention & Hardening

Reduce the chance of this recurring on VMware ESXi 6.7:

• Drive every patch window through vSphere Lifecycle Manager (vLCM) image baselines — image-based remediation has been the supported workflow since vSphere 7 and is the only one that survives a Broadcom subscription audit:

  Connect-VIServer vc01 -User [email protected]
  New-LcmImage -Name 'ESXi-8.0U3-stable' -Version 8.0.3 -BaseImage <build>
  Set-Cluster Prod -LcmImage 'ESXi-8.0U3-stable'
  Get-Cluster Prod | Test-LcmClusterCompliance

• Subscribe to the VMware / Broadcom security advisories feed and forward to your SIEM:

  # Watch the VMSA feed (mirror or scrape via your own collector):
  curl -sSf https://www.vmware.com/security/advisories.xml | head

• Disable SSH and the DCUI on production hosts; enable them only for the patch window. Keep Lockdown Mode on:

  /etc/init.d/SSH stop
  vim-cmd hostsvc/disable_ssh
  vim-cmd hostsvc/lockdown_mode_enter

• Minimise the ESXi firewall surface — disable rulesets you do not need (CIMSLP, cimhttpserver, legacy slpd):

  esxcli network firewall ruleset list
  esxcli network firewall ruleset set --enabled=false --ruleset-id=CIMSLP
  esxcli network firewall ruleset set --enabled=false --ruleset-id=cimhttpserver

• Pin host configurations with a Host Profile and reapply after every patch:

  Connect-VIServer vc01 -User [email protected]
  Get-VMHostProfile
  Apply-VMHostProfile -Entity esx01 -Profile 'Prod-baseline'

• Enable Secure Boot + TPM 2.0 attestation so the hypervisor refuses to load unsigned VIBs or tampered kernel modules:

  esxcli system settings encryption get
  esxcli system security keypersistence enable

• Apply VMware vSphere Security Configuration Guide hardening for VMware ESXi 6.7 and remove unused VIBs.

Related Errors & Cross-Refs

Issues that commonly surface alongside openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide: hostd / vpxa disconnects from vCenter, ramdisk-full conditions on /var/log, vSAN object inaccessibility during reboots, stale DRS recommendations, and VIB acceptance-level mismatches. Useful triage:

esxcli system stats installtime get
esxcli software acceptance get
esxcli storage core device list | head
esxcli vsan health cluster get 2>/dev/null
vdf -h
tail /var/log/vmkernel.log

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References & Further Reading

Primary reference: VMware advisory VMSA-2021-0002. Useful CLI documentation on VMware ESXi 6.7:

esxcli --help
esxcli software --help
esxcli software profile --help
esxcli system maintenanceMode --help
esxcli network firewall --help
vim-cmd help
vmware -lv
vm-support -h

Other resources: docs.vmware.com, VMware Security Advisories index, VMware / Broadcom Knowledge Base, and Broadcom support content notifications for components implicated in openslp — multiple ESXi vulnerabilities (2 CVEs) — VIB / vLCM patch and remediation guide.

View all VMware ESXi 6.7 tutorials on the Tutorials Hub →