CVE-2017-0129 in Lync for Mac
Summary
by MITRE
Microsoft Lync for Mac 2011 fails to properly validate certificates, allowing remote attackers to alter server-client communications, aka "Microsoft Lync for Mac Certificate Validation Vulnerability."
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Analysis
by VulDB Data Team • 12/25/2024
The vulnerability identified as CVE-2017-0129 represents a critical certificate validation flaw in Microsoft Lync for Mac 2011 that fundamentally undermines the security of encrypted communications between client and server components. This weakness resides in the application's inability to properly validate digital certificates presented by servers during the SSL/TLS handshake process, creating a pathway for man-in-the-middle attacks that can compromise the integrity and confidentiality of sensitive communications. The vulnerability specifically affects the certificate validation mechanism within the Lync client implementation on macOS platforms, where the software fails to adequately verify certificate authenticity and trust relationships.
The technical flaw manifests when Lync for Mac 2011 processes server certificates during secure communication establishment. The application's certificate validation logic does not properly enforce certificate chain validation, trust anchor verification, or certificate expiration checks that are fundamental to secure TLS implementations. This allows attackers to present fraudulent certificates that appear valid to the client application, enabling them to intercept, modify, or redirect communications without detection. The vulnerability stems from insufficient certificate validation routines that bypass standard security checks such as certificate signature verification, subject name validation, and certificate revocation status checking, which are core requirements defined by industry standards including those referenced in CWE-295.
The operational impact of this vulnerability extends beyond simple data interception to encompass complete compromise of secure communication channels within enterprise environments. Organizations relying on Lync for Mac 2011 for voice, video, and instant messaging communications face significant risks including unauthorized access to sensitive business information, eavesdropping on confidential conversations, and potential data exfiltration. The vulnerability particularly affects organizations with strict security requirements where communication integrity is paramount, as attackers can manipulate real-time communications without alerting users or administrators. This weakness also enables potential credential theft through session hijacking attacks, as the compromised communication channels can be used to capture authentication tokens or other sensitive data exchanged between users and servers.
Security professionals should implement immediate mitigations including disabling the vulnerable Lync client functionality, deploying network-based certificate monitoring solutions, and ensuring all systems are updated to supported versions of Microsoft Lync or Skype for Business. The vulnerability aligns with ATT&CK technique T1566 which covers credential harvesting through phishing and social engineering, as compromised communications can lead to unauthorized access to corporate resources. Organizations should also consider implementing network segmentation, certificate pinning mechanisms, and enhanced monitoring of TLS handshake activities to detect potential exploitation attempts. The issue demonstrates the critical importance of proper certificate validation in secure communication protocols and highlights the need for comprehensive security testing of client applications that handle sensitive data transmission. Microsoft addressed this vulnerability through security updates that strengthened certificate validation routines and improved trust verification mechanisms in subsequent software releases.