CVE-2021-20106 in Nessus Agent
Summary
by MITRE • 07/21/2021
Nessus Agent versions 8.2.5 and earlier were found to contain a privilege escalation vulnerability which could allow a Nessus administrator user to upload a specially crafted file that could lead to gaining administrator privileges on the Nessus host.
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Analysis
by VulDB Data Team • 07/26/2021
The vulnerability identified as CVE-2021-20106 represents a critical privilege escalation flaw within Nessus Agent versions 8.2.5 and earlier, exposing organizations to significant security risks. This vulnerability specifically targets the administrative functionality of the Nessus scanning platform, where a malicious actor with administrator-level access to the Nessus Agent could exploit a design flaw to escalate their privileges further within the host system. The issue stems from inadequate validation mechanisms during file upload processes, allowing crafted malicious files to be processed with elevated privileges, ultimately enabling unauthorized access to system resources that should be restricted to privileged users only.
The technical exploitation of this vulnerability involves a sophisticated attack vector that leverages the existing administrative access within the Nessus environment. Attackers can upload specially crafted files through the Nessus Agent interface, which then executes with the privileges of the Nessus host process. This flaw essentially creates a pathway for privilege escalation from a standard administrator user to full system administrator privileges, bypassing normal access controls and authorization mechanisms. The vulnerability operates at the application layer and can be classified under CWE-264, which deals with permissions, privileges, and access controls, specifically focusing on inadequate privilege management within software applications.
The operational impact of this vulnerability extends beyond immediate privilege escalation, as it fundamentally compromises the security posture of systems running vulnerable Nessus Agents. Organizations utilizing Nessus for security scanning and vulnerability assessment face potential data breaches, system compromise, and unauthorized access to sensitive information when this vulnerability exists. The attack could result in complete system takeover, allowing threat actors to install backdoors, exfiltrate data, or deploy additional malicious payloads. This vulnerability undermines the trust model of the Nessus platform, as it allows an authenticated user with administrative privileges to gain even more extensive control over the underlying host system, potentially leading to widespread compromise across the network infrastructure.
Security professionals should implement immediate mitigations including upgrading to Nessus Agent versions 8.2.6 and later, which contain patches addressing the privilege escalation vulnerability. Organizations should also enforce strict access controls and monitor file upload activities within their Nessus environments to detect potential exploitation attempts. The remediation process should include comprehensive system auditing and privilege review to ensure no unauthorized access has occurred. Additionally, implementing network segmentation and monitoring solutions can help detect and prevent exploitation attempts. This vulnerability aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', emphasizing the need for robust privilege management and access control mechanisms. Organizations should also consider implementing principle of least privilege models and regular security assessments to prevent similar vulnerabilities from emerging in other security tools and platforms within their infrastructure.