CVE-2015-2319 in Mono
Summary
by MITRE
The TLS stack in Mono before 3.12.1 makes it easier for remote attackers to conduct cipher-downgrade attacks to EXPORT_RSA ciphers via crafted TLS traffic, related to the "FREAK" issue, a different vulnerability than CVE-2015-0204.
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Analysis
by VulDB Data Team • 01/20/2023
The vulnerability identified as CVE-2015-2319 represents a critical weakness in the Transport Layer Security implementation within the Mono framework prior to version 3.12.1. This flaw specifically relates to the FREAK (Factoring RSA Export Keys) vulnerability family, which emerged as a significant threat to secure communications protocols. The issue stems from Mono's TLS stack failing to properly validate cryptographic parameters during the handshake process, creating an avenue for malicious actors to manipulate the encryption negotiation and force the use of weaker cryptographic algorithms.
The technical flaw manifests when the Mono TLS implementation does not adequately enforce cryptographic strength requirements during the TLS handshake phase. Attackers can exploit this weakness by sending specially crafted TLS client hello messages that include support for EXPORT_RSA ciphers, which are typically restricted to 512-bit RSA keys. The vulnerability allows adversaries to downgrade the encryption strength from the expected robust algorithms to these weakened EXPORT_RSA ciphers, effectively undermining the security guarantees that TLS is designed to provide. This particular weakness falls under CWE-327, which addresses the use of weak cryptography, and specifically relates to the improper implementation of cryptographic protocols.
The operational impact of this vulnerability is substantial as it enables remote attackers to conduct cipher-downgrade attacks without requiring any authentication or privileged access. Once successfully exploited, these attacks can allow adversaries to intercept and potentially modify encrypted communications between affected systems. The vulnerability particularly affects environments where Mono-based applications handle sensitive data transmission, including web services, database connections, and any application requiring secure network communications. The attack vector is particularly dangerous because it can be executed over the network without requiring physical access or complex exploitation techniques, making it accessible to a wide range of threat actors.
Organizations utilizing Mono frameworks before version 3.12.1 should prioritize immediate patching and mitigation efforts to address this vulnerability. The recommended remediation involves upgrading to Mono version 3.12.1 or later, which includes fixes specifically addressing the improper TLS cipher negotiation. Security administrators should also implement network monitoring to detect unusual TLS handshake patterns that might indicate attempted exploitation. Additional mitigations include configuring applications to disable support for EXPORT_RSA ciphers, implementing proper cryptographic protocol enforcement, and conducting regular security assessments to identify other potential weaknesses in the TLS implementation. This vulnerability aligns with ATT&CK technique T1071.001, which covers application layer protocol traffic, and represents a critical component of the broader cryptographic attack surface that organizations must address to maintain secure communications infrastructure.