CVE-2019-7477 in SonicOS
Summary
by MITRE
A vulnerability in SonicWall SonicOS and SonicOSv TLS CBC Cipher allow remote attackers to obtain sensitive plaintext data when CBC cipher suites are enabled. This vulnerability affected SonicOS Gen 5 version 5.9.1.10 and earlier, Gen 6 version 6.2.7.3, 6.5.1.3, 6.5.2.2, 6.5.3.1, 6.2.7.8, 6.4.0.0, 6.5.1.8, 6.0.5.3-86o and SonicOSv 6.5.0.2-8v_RC363 (VMWARE), 6.5.0.2.8v_RC367 (AZURE), SonicOSv 6.5.0.2.8v_RC368 (AWS), SonicOSv 6.5.0.2.8v_RC366 (HYPER_V).
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Analysis
by VulDB Data Team • 05/23/2020
The vulnerability identified as CVE-2019-7477 represents a critical weakness in SonicWall SonicOS and SonicOSv implementations that specifically targets the Transport Layer Security protocol's Cipher Block Chaining mode. This flaw enables remote attackers to extract sensitive plaintext information from encrypted communications when CBC cipher suites are active within the network infrastructure. The vulnerability stems from improper implementation of the TLS protocol stack, creating a pathway for attackers to exploit weaknesses in the cryptographic processing mechanisms that protect network traffic. The affected systems operate with SonicOS versions that have not adequately addressed the inherent security issues present in the CBC encryption mode, making them susceptible to sophisticated attacks that can compromise the confidentiality of transmitted data.
The technical root cause of this vulnerability lies in the improper handling of TLS CBC cipher suites within the SonicWall firewall implementations. This flaw manifests as a padding oracle attack vector that allows adversaries to systematically decrypt sensitive data through repeated requests and analysis of response behaviors. The vulnerability specifically impacts the way the system processes encrypted packets when CBC mode is enabled, creating opportunities for attackers to manipulate the encryption process and recover plaintext information. This weakness aligns with CWE-327, which addresses the use of weak cryptographic algorithms and improper implementation of cryptographic protocols, and represents a classic example of how CBC mode implementations can be compromised when proper security controls are not enforced. The attack typically involves sending specially crafted requests to the vulnerable system and analyzing the timing variations or error responses that reveal information about the decrypted content.
The operational impact of CVE-2019-7477 extends beyond simple data exposure, as it can compromise the integrity of the entire network security posture maintained by SonicWall deployments. Organizations utilizing affected SonicOS versions face significant risks including unauthorized access to confidential communications, potential credential theft, and exposure of sensitive business information that flows through the network infrastructure. The vulnerability affects multiple generations of SonicWall appliances and virtual machines, creating widespread exposure across various deployment scenarios including enterprise networks, cloud environments, and hybrid infrastructure configurations. Attackers can leverage this weakness to perform reconnaissance activities that may lead to more extensive compromise of the network perimeter, as the ability to decrypt communications undermines fundamental security controls that organizations rely upon for protecting their data assets.
Organizations should immediately implement mitigations including disabling CBC cipher suites on affected SonicWall systems and upgrading to patched versions of SonicOS that address the underlying cryptographic implementation issues. The recommended approach involves configuring the firewall to use only secure cipher suites that do not employ CBC mode, specifically avoiding the use of TLS_RSA_WITH_AES_128_CBC_SHA and similar vulnerable cipher suites. Network administrators should also consider implementing additional monitoring controls to detect anomalous traffic patterns that might indicate exploitation attempts. This vulnerability demonstrates the critical importance of proper cryptographic implementation and adherence to security best practices as outlined in the NIST SP 800-52 guidelines for TLS configuration. Organizations must also consider the broader implications of this vulnerability within their security frameworks and ensure that their incident response procedures include specific protocols for addressing cryptographic weaknesses in network infrastructure components.