CVE-2019-5102 in OpenWrt
Summary
by MITRE
An exploitable information leak vulnerability exists in the ustream-ssl library of OpenWrt, versions 18.06.4 and 15.05.1. When connecting to a remote server, the server's SSL certificate is checked but no action is taken when the certificate is invalid. An attacker could exploit this behavior by performing a man-in-the-middle attack, providing any certificate, leading to the theft of all the data sent by the client during the first request.
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Analysis
by VulDB Data Team • 02/23/2024
The vulnerability described in CVE-2019-5102 represents a critical security flaw within the ustream-ssl library component of OpenWrt operating systems. This issue affects specifically versions 18.06.4 and 15.05.1, creating a dangerous condition where the system performs SSL certificate validation but fails to enforce proper certificate validation policies. The flaw stems from the library's inability to properly handle certificate validation failures, allowing malicious actors to bypass security measures that should prevent unauthorized access to network communications.
The technical implementation of this vulnerability manifests in the SSL/TLS handshake process where the ustream-ssl library validates server certificates but does not properly terminate connections when certificate validation fails. This behavior creates a dangerous trust model where any certificate, regardless of validity, is accepted by the client. The flaw operates at the transport layer security validation mechanism, where the library should enforce certificate chain validation, hostname verification, and certificate expiration checks but fails to implement these critical security controls. According to CWE-295, this represents a weakness in certificate validation that directly enables man-in-the-middle attacks by allowing certificate validation bypass.
The operational impact of this vulnerability extends beyond simple data interception to create a complete breakdown in secure communication protocols. When a client establishes a connection to a server through the vulnerable ustream-ssl library, the attacker can perform a man-in-the-middle attack by presenting a fake certificate that appears valid to the client. This allows the attacker to transparently intercept, modify, and steal all data transmitted during the initial connection phase, including sensitive authentication credentials, personal information, and confidential business data. The vulnerability specifically affects the first request made during a session, making it particularly dangerous for applications that rely on initial authentication or data exchange. This flaw directly aligns with ATT&CK technique T1041 which describes data compression and encryption for exfiltration, as the stolen data can be easily captured and transmitted without detection.
The exploitation of this vulnerability requires minimal technical expertise and can be executed through standard network attack tools that can intercept and retransmit SSL connections. Attackers can leverage this weakness to perform credential theft, session hijacking, and data exfiltration attacks against systems using vulnerable OpenWrt versions. The impact is particularly severe for IoT devices and network appliances that rely on OpenWrt as their operating system, as these devices often handle sensitive network communications and may not have additional security layers to protect against such attacks. Organizations should consider implementing network segmentation, monitoring for unusual SSL certificate behavior, and deploying intrusion detection systems to identify potential exploitation attempts. The recommended mitigation strategy involves upgrading to patched versions of OpenWrt, implementing proper certificate validation policies, and ensuring that all SSL/TLS connections enforce strict certificate validation procedures. Additionally, network administrators should consider implementing certificate pinning mechanisms and monitoring for certificate validation failures to detect potential exploitation attempts.