CVE-2019-0798 in Lync Server
Summary
by MITRE
A spoofing vulnerability exists when a Lync Server or Skype for Business Server does not properly sanitize a specially crafted request, aka 'Skype for Business and Lync Spoofing Vulnerability'.
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Analysis
by VulDB Data Team • 05/16/2020
The CVE-2019-0798 vulnerability represents a critical spoofing flaw in Microsoft Lync Server and Skype for Business Server implementations that fundamentally undermines the integrity of communication protocols. This vulnerability arises from insufficient input validation and sanitization mechanisms within the server's handling of specially crafted requests, creating an avenue for malicious actors to manipulate authentication and session management processes. The flaw specifically impacts the authentication flow where the servers fail to properly validate and sanitize user-provided data, allowing attackers to craft requests that bypass normal security controls and potentially impersonate legitimate users within the communication infrastructure.
The technical exploitation of this vulnerability stems from the server's inadequate sanitization of input parameters within the communication protocols used by Lync and Skype for Business. When the server receives a crafted request containing maliciously formatted data, it processes this information without sufficient validation, leading to potential manipulation of session identifiers, user authentication tokens, or other critical communication metadata. This flaw operates at the protocol level where the server's trust model is compromised, enabling attackers to inject false information that appears legitimate to the system's internal validation mechanisms. The vulnerability is particularly concerning because it affects core authentication and session management functions that are fundamental to secure communication platforms.
From an operational impact perspective, this vulnerability creates significant risks for organizations relying on Lync Server or Skype for Business Server for enterprise communications. Attackers who successfully exploit this flaw can potentially establish unauthorized sessions, intercept or manipulate communication traffic, and gain access to sensitive business communications. The spoofing capability allows malicious actors to impersonate legitimate users, potentially leading to data exfiltration, man-in-the-middle attacks, or disruption of critical business communications. Organizations may experience unauthorized access to confidential conversations, credential compromise, and potential lateral movement within their network infrastructure through the compromised communication channels.
Security professionals should implement multiple layers of mitigation strategies to address this vulnerability effectively. Immediate remediation efforts should focus on applying Microsoft security patches and updates to affected systems, as the vulnerability was addressed through official Microsoft security releases. Network segmentation and monitoring should be enhanced to detect anomalous authentication patterns or unusual request behaviors that might indicate exploitation attempts. Implementing strict input validation controls and rate limiting mechanisms can help prevent exploitation attempts, while regular security assessments should verify that the sanitization processes are properly configured. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a significant concern for organizations following ATT&CK framework's credential access and privilege escalation techniques. Additionally, implementing robust logging and monitoring solutions that track authentication events and session management activities can provide early detection capabilities for potential exploitation attempts, while maintaining compliance with security standards such as NIST SP 800-53 and ISO 27001 requirements for secure communication systems.