CVE-2020-14929 in Mail Client
Summary
by MITRE
Alpine before 2.23 silently proceeds to use an insecure connection after a /tls is sent in certain circumstances involving PREAUTH, which is a less secure behavior than the alternative of closing the connection and letting the user decide what they would like to do.
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Analysis
by VulDB Data Team • 03/20/2025
The vulnerability identified as CVE-2020-14929 affects Alpine versions prior to 2.23 and represents a significant security flaw in the handling of TLS connections during the pre-authentication phase. This issue stems from the software's failure to properly terminate connections when encountering insecure TLS negotiation attempts, creating a dangerous precedent where the system continues operating with weakened security rather than rejecting potentially compromised communications. The vulnerability specifically manifests when the /tls command is issued in certain pre-authentication scenarios, demonstrating a design flaw that prioritizes system availability over security integrity.
The technical implementation of this vulnerability involves the Alpine software's TLS handshake process where the system does not adequately validate the security parameters during the initial connection phase. When a client sends a /tls command before authentication, the vulnerable version of Alpine fails to properly assess the security context and instead chooses to proceed with an insecure connection rather than terminating the session or requiring a secure handshake. This behavior creates a man-in-the-middle attack vector where adversaries can potentially downgrade the security level of communications, violating fundamental security principles of connection integrity. The flaw operates at the protocol level, affecting how the software handles cryptographic negotiations and connection state management.
From an operational perspective, this vulnerability exposes systems to significant risk during the pre-authentication phase where sensitive information might be transmitted over insecure channels. The silent continuation of insecure connections means that administrators and users remain unaware of the compromised security state, creating a false sense of security while actual communications may be vulnerable to interception or manipulation. This issue particularly impacts environments where Alpine is used for network services or applications requiring secure communications, as it undermines the trust model that users expect from properly configured security protocols. The vulnerability's impact extends beyond immediate data exposure to potentially enable further exploitation through credential theft or session hijacking attacks.
Security practitioners should prioritize immediate patching of affected Alpine installations to version 2.23 or later where this behavior has been corrected. The mitigation strategy should include comprehensive network monitoring to detect any unusual TLS behavior patterns and implementation of connection logging to identify potential exploitation attempts. Organizations should also review their pre-authentication security policies and ensure proper TLS enforcement mechanisms are in place. This vulnerability aligns with CWE-319 (CWE-319: Cleartext Transmission of Sensitive Information) and represents a specific implementation weakness that could be categorized under ATT&CK technique T1046 (Network Service Scanning) when exploited by attackers seeking to identify vulnerable systems. The remediation process should include thorough testing of patched environments to ensure that proper TLS termination behavior is maintained while preserving legitimate functionality.