CVE-2006-0956 in NuFW
Summary
by MITRE
nuauth in NuFW before 1.0.21 does not properly handle blocking TLS sockets, which allows remote authenticated users to cause a denial of service (service hang) by flooding packets at the authentication server.
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Analysis
by VulDB Data Team • 07/20/2018
The vulnerability described in CVE-2006-0956 affects the nuauth component within NuFW version 1.0.20 and earlier, representing a critical flaw in the network firewall's authentication handling mechanism. This issue specifically targets the TLS socket management functionality that NuFW employs for secure authentication processes. The vulnerability stems from inadequate processing of TLS socket states during the authentication phase, creating a potential attack vector that can be exploited by authenticated remote adversaries. The flaw manifests when legitimate users who have successfully authenticated to the system can subsequently flood the authentication server with crafted packets, leading to a complete service hang condition that effectively renders the firewall's authentication capabilities unusable.
The technical root cause of this vulnerability lies in the improper handling of TLS socket connections within the nuauth module, which operates as a critical authentication daemon for the NuFW system. When remote authenticated users send a high volume of packets to the authentication server, the system fails to properly manage the socket states and connection handling mechanisms. This results in a resource exhaustion scenario where the server becomes overwhelmed with pending connections or stuck in processing states that prevent normal authentication operations. The vulnerability specifically impacts the TLS socket blocking mechanism, where the system does not adequately implement proper timeout handling or connection state management when processing authenticated user requests. This mismanagement creates a condition where the authentication server becomes unresponsive to legitimate authentication requests, effectively causing a denial of service that can be triggered by authenticated users who are already within the system's trust boundary.
The operational impact of this vulnerability extends beyond simple service disruption to create a significant security risk within the network infrastructure. An authenticated attacker can leverage this flaw to perform a targeted denial of service attack against the authentication server, potentially compromising the entire firewall's ability to authenticate new users or validate existing sessions. The attack requires only authenticated access to the system, making it particularly dangerous as it can be executed by insiders or compromised legitimate users. The service hang condition created by this vulnerability can persist until the system is manually restarted or the affected processes are terminated, leading to extended downtime for network access control. This vulnerability directly impacts the availability and integrity of the authentication service, potentially allowing unauthorized access to network resources if the authentication system becomes unavailable for legitimate users.
Mitigation strategies for CVE-2006-0956 focus primarily on upgrading to NuFW version 1.0.21 or later, where the TLS socket handling has been properly implemented to prevent the resource exhaustion condition. Network administrators should implement rate limiting mechanisms at the authentication server level to prevent packet flooding attacks from authenticated users, though this approach provides only partial protection. The vulnerability aligns with CWE-400, which addresses uncontrolled resource consumption, and can be mapped to ATT&CK technique T1499.004 for network denial of service attacks. Additionally, implementing proper monitoring and alerting for unusual authentication server behavior can help detect exploitation attempts before they cause complete service outages. Security configurations should include limiting the number of concurrent authenticated connections and implementing proper timeout mechanisms for TLS socket operations to prevent the accumulation of stale connections that contribute to the service hang condition.