CVE-2021-25274: SolarWinds Orion Platform RCE Flaw

CVE-2021-25274 Overview

CVE-2021-25274 is a critical insecure deserialization vulnerability affecting the Collector Service in SolarWinds Orion Platform versions prior to 2020.2.4. The vulnerability exists because the Collector Service uses Microsoft Message Queue (MSMQ) without properly configuring permissions on its private queues. This allows remote unauthenticated attackers to send malicious messages to TCP port 1801, which the Collector Service processes and deserializes in an insecure manner. Successful exploitation results in arbitrary code execution with LocalSystem privileges, granting complete control over the affected system.

Critical Impact

Remote unauthenticated attackers can achieve full system compromise by exploiting insecure MSMQ queue permissions and unsafe deserialization to execute arbitrary code as LocalSystem.

Affected Products

• SolarWinds Orion Platform versions before 2020.2.4
• Systems with MSMQ service enabled on TCP port 1801
• Collector Service component within SolarWinds Orion deployments

Discovery Timeline

• 2021-02-03 - CVE-2021-25274 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-25274

Vulnerability Analysis

This vulnerability stems from two interconnected security flaws in the SolarWinds Orion Platform's Collector Service. First, the service utilizes Microsoft Message Queue (MSMQ) for inter-process communication but fails to implement proper access controls on its private message queues. This means any network-accessible client can connect to TCP port 1801 and submit messages without authentication.

The second and more severe flaw involves how the Collector Service processes incoming messages. When messages arrive in the queue, the service deserializes them using an insecure deserialization mechanism. This allows attackers to craft specially constructed serialized objects that, when deserialized, execute arbitrary code within the context of the Collector Service—which runs as LocalSystem.

The combination of unauthenticated network access and insecure deserialization creates a highly exploitable attack chain. An attacker with network access to the MSMQ port can achieve complete system compromise without any credentials or prior authentication.

Root Cause

The root cause of CVE-2021-25274 is twofold: improper access control configuration on MSMQ private queues and the use of insecure deserialization practices (CWE-502: Deserialization of Untrusted Data). The Collector Service does not validate or restrict which clients can send messages to its queue, and it does not implement safe deserialization techniques to prevent object injection attacks.

Attack Vector

The attack vector is network-based, requiring only TCP connectivity to port 1801 where MSMQ listens. An attacker can exploit this vulnerability remotely without authentication by sending a crafted message containing a malicious serialized payload. When the Collector Service processes this message, the unsafe deserialization triggers execution of the attacker's payload with LocalSystem privileges.

The attack flow involves:

1. Establishing a TCP connection to port 1801 on the target system
2. Sending a specially crafted MSMQ message containing a malicious serialized .NET object
3. The Collector Service receives and deserializes the message without validation
4. The malicious payload executes with LocalSystem privileges

For detailed technical analysis of this vulnerability, refer to the Trustwave SpiderLabs security advisory.

Detection Methods for CVE-2021-25274

Indicators of Compromise

• Unexpected network connections to TCP port 1801 from external or unauthorized systems
• Anomalous process spawning from the SolarWinds Collector Service (SolarWinds.Collector.Service.exe)
• Unusual MSMQ activity or queue message patterns indicating serialized object payloads
• Evidence of code execution or privilege escalation originating from LocalSystem context

Detection Strategies

• Monitor network traffic to TCP port 1801 for connections from unauthorized or external IP addresses
• Implement EDR monitoring for suspicious child processes spawned by SolarWinds.Collector.Service.exe
• Review Windows Event Logs for MSMQ-related events and service anomalies
• Deploy network segmentation rules and alerts for MSMQ traffic crossing security boundaries

Monitoring Recommendations

• Enable detailed logging for the SolarWinds Collector Service and MSMQ components
• Implement network-level monitoring and alerting for TCP port 1801 access patterns
• Use behavioral analysis to detect unusual process execution chains from the Collector Service
• Correlate authentication logs with MSMQ activity to identify unauthenticated access attempts

How to Mitigate CVE-2021-25274

Immediate Actions Required

• Upgrade SolarWinds Orion Platform to version 2020.2.4 or later immediately
• Restrict network access to TCP port 1801 using firewall rules to allow only trusted systems
• Disable MSMQ if not required for operational functionality
• Isolate SolarWinds Orion servers in a dedicated network segment with strict access controls

Patch Information

SolarWinds has released version 2020.2.4 of the Orion Platform which addresses this vulnerability. Organizations should prioritize upgrading to this version or later. Review the Trustwave SpiderLabs advisory for additional technical context on the vulnerability and remediation.

Workarounds

• Block inbound connections to TCP port 1801 at the network perimeter and host-based firewalls
• Implement network segmentation to restrict MSMQ access to only authorized internal systems
• Consider disabling the Message Queuing (MSMQ) Windows feature if not operationally required
• Apply the principle of least privilege to the Collector Service account where possible

# Firewall rule to block external MSMQ access (Windows)
netsh advfirewall firewall add rule name="Block MSMQ External" dir=in action=block protocol=tcp localport=1801 profile=public,private