CVE-2006-2093 in Nessus
Summary
by MITRE
Nessus before 2.2.8, and 3.x before 3.0.3, allows user-assisted attackers to cause a denial of service (memory consumption) via a NASL script that calls split with an invalid sep parameter. NOTE: a design goal of the NASL language is to facilitate sharing of security tests by guaranteeing that a script "can not do anything nasty." This issue is appropriate for CVE only if Nessus users have an expectation that a split statement will not use excessive memory.
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Analysis
by VulDB Data Team • 06/18/2019
The vulnerability described in CVE-2006-2093 affects Nessus network security scanning software versions prior to 2.2.8 and 3.0.3, representing a critical denial of service weakness in the Network Asset Security Language (NASL) scripting environment. This issue demonstrates a fundamental flaw in the security software's design philosophy where the expectation of safe script execution is violated through a seemingly benign function call. The vulnerability specifically targets the split function within NASL, which is intended to be a safe utility for parsing strings but becomes exploitable when provided with invalid parameters. The flaw operates by allowing malicious actors to craft NASL scripts that consume excessive memory resources through improper parameter handling, effectively causing the Nessus scanner to exhaust available memory and become unresponsive.
The technical implementation of this vulnerability stems from inadequate input validation within the NASL interpreter's split function implementation. When an attacker provides an invalid separator parameter to the split function, the underlying memory management mechanism fails to properly handle the malformed input, leading to unbounded memory allocation patterns. This represents a classic buffer over-read or improper resource management issue that falls under the CWE-122 category of improper restriction of operations within a memory buffer. The vulnerability is classified as user-assisted because it requires an attacker to either upload or execute a malicious NASL script, but the impact is severe enough to compromise the availability of the entire scanning infrastructure. The design principle that NASL scripts should be incapable of performing malicious operations is fundamentally violated, as this particular function call creates a legitimate attack vector that can be exploited by users with access to the Nessus scripting environment.
The operational impact of CVE-2006-2093 extends beyond simple service disruption to potentially compromise the entire network security monitoring capability of organizations relying on Nessus for vulnerability assessment. When the memory consumption reaches critical levels, the Nessus scanner becomes unresponsive and may crash entirely, requiring manual intervention to restore service. This vulnerability particularly affects environments where Nessus is used for continuous monitoring, as a successful attack could result in extended periods of network visibility loss. The issue is especially concerning in enterprise environments where multiple security analysts may have access to upload custom scripts, creating potential attack vectors through social engineering or privilege escalation scenarios. The vulnerability also impacts the software's reputation and trustworthiness, as it contradicts the fundamental security assumptions that users make about the safety of the scripting environment. Organizations may experience cascading effects where the denial of service impacts other security tools that depend on Nessus for baseline vulnerability intelligence.
Mitigation strategies for CVE-2006-2093 require both immediate patching and architectural considerations to prevent similar vulnerabilities in the future. The most effective immediate solution is upgrading Nessus to version 2.2.8 or 3.0.3, which contain proper input validation for the split function. Organizations should also implement strict access controls for NASL script uploads and execution, limiting privileges to trusted administrators only. Additionally, implementing memory monitoring and resource limits on Nessus processes can help detect and prevent excessive memory consumption patterns before they cause complete system failure. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks, where adversaries leverage legitimate software features to consume resources. The vulnerability demonstrates the importance of input validation and proper resource management in security tools, as outlined in the CWE taxonomy and industry best practices for secure coding. Organizations should also consider implementing automated script analysis and sandboxing mechanisms to prevent malicious script execution before they can impact system resources.