CVE-2020-5138 in SonicOS
Summary
by MITRE • 10/12/2020
A Heap Overflow vulnerability in the SonicOS allows a remote unauthenticated attacker to cause Denial of Service (DoS) on the firewall SSLVPN service and leads to SonicOS crash. This vulnerability affected SonicOS Gen 5 version 5.9.1.7, 5.9.1.13, Gen 6 version 6.5.4.7, 6.5.1.12, 6.0.5.3, SonicOSv 6.5.4.v and Gen 7 version SonicOS 7.0.0.0.
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Analysis
by VulDB Data Team • 11/18/2020
The heap overflow vulnerability identified as CVE-2020-5138 represents a critical security flaw within SonicWall's SonicOS firewall operating system that specifically targets the SSLVPN service functionality. This vulnerability exists in multiple generations of SonicOS including versions 5.9.1.7, 5.9.1.13, 6.5.4.7, 6.5.1.12, 6.0.5.3, SonicOSv 6.5.4.v, and SonicOS 7.0.0.0, affecting both hardware and virtualized deployments. The flaw manifests as a heap-based buffer overflow condition that can be exploited by remote attackers without requiring authentication credentials, making it particularly dangerous for network security infrastructure. This vulnerability directly impacts the core SSLVPN service functionality, which is essential for secure remote access to corporate networks through SonicWall firewalls.
The technical implementation of this heap overflow occurs when the SonicOS SSLVPN service processes malformed or specially crafted input data that exceeds the allocated heap memory boundaries. The vulnerability stems from inadequate input validation and memory management within the SSLVPN component of the SonicOS operating system, creating conditions where attacker-controlled data can overwrite adjacent heap memory regions. This type of vulnerability maps directly to CWE-121 Heap-based Buffer Overflow, which is classified as a common weakness in software development practices. The overflow condition specifically affects the heap allocation mechanisms used by the SSLVPN service, causing memory corruption that ultimately leads to application instability and system crashes.
The operational impact of CVE-2020-5138 extends beyond simple service disruption to create significant business continuity risks for organizations relying on SonicWall firewalls for remote access security. When exploited, the vulnerability results in complete denial of service conditions where the SSLVPN service becomes unavailable, effectively blocking legitimate remote access attempts for authorized users. The crash conditions can occur during normal SSLVPN connection establishment or authentication processes, making it difficult for administrators to predict or prevent the attacks. Organizations may experience extended downtime periods while system recovery procedures are implemented, potentially disrupting critical business operations that depend on secure remote access capabilities. The vulnerability's remote exploitability without authentication means that attackers can target these systems from anywhere on the internet, amplifying the potential impact across all organizations with affected SonicWall deployments.
Mitigation strategies for CVE-2020-5138 should prioritize immediate patch deployment from SonicWall, as the vendor has released security updates specifically addressing this heap overflow condition. Organizations should also implement network segmentation to limit exposure of vulnerable SonicWall devices to untrusted networks, while monitoring network traffic for suspicious patterns that may indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under T1190 Exploit Public-Facing Application, highlighting the need for proper network monitoring and intrusion detection systems. Additional defensive measures include disabling SSLVPN services when not actively required, implementing strict firewall rules to limit access to SSLVPN ports, and maintaining detailed logging of SSLVPN authentication attempts. Security teams should also conduct vulnerability assessments to identify all instances of affected SonicOS versions within their environment and establish incident response procedures specifically tailored to handle SSLVPN service outages caused by heap overflow exploits.