CVE-2021-20100 in Nessus Agent
Summary
by MITRE • 06/28/2021
Nessus Agent 8.2.4 and earlier for Windows were found to contain multiple local privilege escalation vulnerabilities which could allow an authenticated, local administrator to run specific Windows executables as the Nessus host. This is different than CVE-2021-20099.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 07/03/2021
The vulnerability identified as CVE-2021-20100 affects Nessus Agent versions 8.2.4 and earlier on Windows systems, representing a critical local privilege escalation flaw that undermines the security posture of organizations relying on Tenable's vulnerability scanning solution. This vulnerability specifically targets the Windows implementation of the Nessus Agent and creates a pathway for authenticated local administrators to execute specific Windows executables with elevated privileges equivalent to those of the Nessus host process. Unlike CVE-2021-20099 which addresses different aspects of the same product, this vulnerability focuses specifically on the privilege escalation mechanism within the agent's execution environment.
The technical flaw stems from improper privilege handling within the Nessus Agent's Windows implementation, where the agent fails to properly validate or restrict execution contexts when running specific Windows executables. This weakness allows a local administrator who has authenticated to the system to leverage the agent's existing privileges to escalate their access level. The vulnerability manifests when the Nessus Agent processes certain executable files or commands, potentially enabling an attacker to execute malicious code with the elevated privileges of the host process. This represents a classic privilege escalation vector where the agent's operational context provides unintended access to higher privilege execution paths.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates a potential attack surface that could be exploited by malicious actors within an organization's network. An authenticated local administrator who discovers this vulnerability could potentially use it to gain broader system access, escalate privileges further, or establish persistence mechanisms within the environment. The vulnerability's exploitation requires local access and authentication, but once achieved, it could enable attackers to move laterally within the network or maintain access to critical systems. This risk is particularly concerning given that Nessus Agents are commonly deployed across enterprise environments for continuous vulnerability assessment and monitoring.
Organizations should immediately update their Nessus Agent installations to versions beyond 8.2.4 to remediate this vulnerability, as the flaw affects the core functionality of the agent's Windows implementation. System administrators should also conduct thorough inventory checks to identify all affected systems and ensure proper patch management procedures are in place. The vulnerability aligns with CWE-276, which addresses improper privileges, and represents a significant concern from an ATT&CK framework perspective under privilege escalation techniques. Security teams should monitor for any suspicious execution patterns or unauthorized privilege changes within their Nessus agent environments, as this vulnerability could be leveraged as part of broader attack campaigns targeting enterprise security infrastructure.