CVE-2023-0524: Tenable Nessus Privilege Escalation Flaw

CVE-2023-0524 Overview

CVE-2023-0524 is a privilege escalation vulnerability identified in Tenable's security scanning products. As part of Tenable's Security Development Lifecycle, an internal review discovered that a malicious actor with sufficient permissions could modify environment variables and abuse an impacted plugin in order to escalate privileges. While Tenable notes that the probability of successful exploitation is low, the potential impact of privilege escalation in security scanning infrastructure makes this a significant concern for organizations relying on these products.

Critical Impact

Attackers with low-level access could exploit this vulnerability to escalate privileges on systems running Tenable Nessus, Tenable.io, or Tenable.sc, potentially compromising the integrity of security scanning operations and gaining unauthorized access to sensitive vulnerability data.

Affected Products

• Tenable Nessus (versions prior to plugin feed serial #202212212055)
• Tenable Tenable.io (versions prior to plugin feed serial #202212212055)
• Tenable Tenable.sc (versions prior to plugin feed serial #202212212055)

Discovery Timeline

• 2023-02-01 - CVE-2023-0524 published to NVD
• 2025-03-27 - Last updated in NVD database

Technical Details for CVE-2023-0524

Vulnerability Analysis

This privilege escalation vulnerability (CWE-269: Improper Privilege Management) exists within Tenable's plugin architecture. The flaw allows an authenticated attacker with low privileges to manipulate the execution context of security scanning plugins through environment variable modification. The attack can be executed remotely over the network without user interaction, and successful exploitation could result in complete compromise of the confidentiality, integrity, and availability of the affected system.

The vulnerability requires the attacker to have legitimate but limited access to the affected Tenable product. From this position, they can modify environment variables that influence how plugins execute, potentially allowing them to run code with elevated privileges within the scanning infrastructure.

Root Cause

The root cause stems from improper privilege management (CWE-269) in how the affected Tenable products handle environment variables during plugin execution. The plugin architecture did not sufficiently validate or sanitize environment variable inputs, allowing lower-privileged users to influence the execution context of plugins that run with higher privileges. This insufficient separation between user-controlled inputs and privileged execution paths created the conditions for privilege escalation.

Attack Vector

The attack vector is network-based and requires authenticated access with low-level privileges. An attacker would first need to obtain valid credentials for the Tenable product, then identify and target vulnerable plugins that can be influenced through environment variable manipulation.

The exploitation flow involves:

1. Authenticating to the Tenable product with limited privileges
2. Identifying environment variables that influence plugin execution
3. Modifying these environment variables to inject malicious values
4. Triggering the execution of a vulnerable plugin
5. The plugin executes with elevated privileges, carrying the attacker's payload

Since no verified code examples are available for this vulnerability, organizations should refer to the Tenable Security Advisory TNS-2023-04 for specific technical details about the exploitation mechanism.

Detection Methods for CVE-2023-0524

Indicators of Compromise

• Unexpected modifications to environment variables on systems running Tenable products
• Anomalous plugin execution patterns or unusual plugin behavior
• Log entries showing privilege escalation attempts or unauthorized administrative actions
• Unexplained changes to user privilege levels within Tenable applications

Detection Strategies

• Monitor Tenable product logs for unusual environment variable modifications before plugin execution
• Implement behavioral analysis to detect privilege escalation attempts within the scanning infrastructure
• Review audit logs for users accessing administrative functions without appropriate authorization
• Deploy endpoint detection solutions to identify suspicious process spawning from Tenable services

Monitoring Recommendations

• Enable verbose logging on all Tenable products to capture environment variable interactions
• Configure SIEM alerts for privilege escalation indicators within vulnerability scanning systems
• Establish baseline behavior for plugin execution and alert on deviations
• Regularly audit user permissions and access levels within Tenable products

How to Mitigate CVE-2023-0524

Immediate Actions Required

• Update Tenable plugin feeds to serial number #202212212055 or greater immediately
• Review and restrict user permissions on Tenable products to enforce least privilege
• Audit all accounts with access to Tenable products and remove unnecessary privileges
• Monitor for any signs of prior exploitation using the detection strategies outlined above

Patch Information

Tenable has resolved this vulnerability and distributed updates via the Tenable plugin feed. Organizations should ensure their plugin feed serial number is equal to or greater than #202212212055. Tenable has also implemented several defense-in-depth fixes alongside the primary remediation. For complete patch details and verification instructions, consult the Tenable Security Advisory TNS-2023-04.

Workarounds

• Implement strict network segmentation to limit access to Tenable management interfaces
• Enforce multi-factor authentication for all Tenable product access
• Restrict administrative access to dedicated management networks only
• Consider disabling or restricting untrusted plugins until updates can be applied

# Verify Tenable plugin feed version
# Check that your feed serial is >= 202212212055
# In Nessus, navigate to Settings > Software Update
# Or via CLI, check the plugin feed version:
/opt/nessus/sbin/nessuscli update --plugins-only
/opt/nessus/sbin/nessuscli info