CVE-2017-3807 in ASA
Summary
by MITRE
A vulnerability in Common Internet Filesystem (CIFS) code in the Clientless SSL VPN functionality of Cisco ASA Software, Major Releases 9.0-9.6, could allow an authenticated, remote attacker to cause a heap overflow. The vulnerability is due to insufficient validation of user supplied input. An attacker could exploit this vulnerability by sending a crafted URL to the affected system. An exploit could allow the remote attacker to cause a reload of the affected system or potentially execute code. Note: Only traffic directed to the affected system can be used to exploit this vulnerability. This vulnerability affects systems configured in routed firewall mode only and in single or multiple context mode. This vulnerability can be triggered by IPv4 or IPv6 traffic. A valid TCP connection is needed to perform the attack. The attacker needs to have valid credentials to log in to the Clientless SSL VPN portal. Vulnerable Cisco ASA Software running on the following products may be affected by this vulnerability: Cisco ASA 5500 Series Adaptive Security Appliances, Cisco ASA 5500-X Series Next-Generation Firewalls, Cisco Adaptive Security Virtual Appliance (ASAv), Cisco ASA for Firepower 9300 Series, Cisco ASA for Firepower 4100 Series. Cisco Bug IDs: CSCvc23838.
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Analysis
by VulDB Data Team • 08/28/2024
The vulnerability described in CVE-2017-3807 represents a critical heap overflow condition within the Common Internet Filesystem implementation of Cisco Adaptive Security Appliance (ASA) software versions 9.0 through 9.6. This flaw exists specifically within the Clientless SSL VPN functionality, which allows remote users to access network resources without requiring a dedicated VPN client software. The vulnerability stems from inadequate input validation mechanisms that fail to properly sanitize user-supplied data, creating a pathway for malicious exploitation through carefully crafted URLs. The heap overflow condition occurs when the system processes malformed input through the CIFS code pathway, potentially leading to system instability or unauthorized code execution. This vulnerability demonstrates a classic weakness in software security architecture where insufficient boundary checking and input sanitization creates opportunities for memory corruption attacks.
The technical exploitation of this vulnerability requires specific prerequisites that limit its attack surface while maintaining significant risk. An authenticated attacker must first establish valid credentials to access the Clientless SSL VPN portal, as the vulnerability cannot be triggered without proper authentication. The attack vector specifically requires sending a crafted URL to the affected system, which then processes this input through the vulnerable CIFS code path. The exploit necessitates an active TCP connection and can be initiated through either IPv4 or IPv6 traffic protocols, demonstrating the broad applicability of the vulnerability across different network configurations. The system must be operating in routed firewall mode with either single or multiple context configurations to be affected, indicating that the vulnerability is specifically tied to certain operational modes rather than being a universal flaw across all Cisco ASA deployments. This authentication requirement provides some mitigation but does not eliminate the serious security implications for systems with compromised credentials or insider threats.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable complete system compromise. When exploited successfully, the heap overflow can cause the affected Cisco ASA system to reload automatically, creating denial of service conditions that disrupt network security services. More critically, the vulnerability could allow remote code execution, enabling attackers to gain unauthorized control over the affected system and potentially escalate privileges to access underlying network resources. The affected platforms include multiple Cisco ASA series including the 5500 Series Adaptive Security Appliances, 5500-X Series Next-Generation Firewalls, Adaptive Security Virtual Appliance, and various Firepower series appliances. This widespread impact across different hardware platforms indicates the severity of the vulnerability and the potential for significant disruption to enterprise network security infrastructure. The vulnerability's presence in Clientless SSL VPN functionality particularly impacts organizations that rely on remote access capabilities, as it creates a potential attack vector that could compromise network access controls.
Organizations affected by this vulnerability should implement immediate mitigations while planning for proper software updates and patches. The recommended approach involves applying the official Cisco security patches that address the input validation deficiencies in the CIFS code implementation. Network administrators should also consider implementing additional access controls and monitoring for suspicious URL traffic patterns that might indicate exploitation attempts. The vulnerability's requirement for authenticated access provides a window of opportunity for detection through unusual login patterns or network behavior monitoring. Security teams should also evaluate their current network segmentation strategies to limit the potential impact if exploitation occurs, particularly in environments where the ASA serves as a critical security gateway. This vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a typical example of how insufficient input validation can create persistent security weaknesses in network infrastructure software. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service techniques, as it enables both system compromise and availability disruption. Organizations should also consider implementing network-based intrusion detection systems that can identify and alert on potential exploitation attempts through the specific URL patterns that trigger this vulnerability, providing an additional layer of defense against unauthorized access attempts.