CVE-2018-8558 in Office
Summary
by MITRE
An information disclosure vulnerability exists when Microsoft Outlook fails to respect "Default link type" settings configured via the SharePoint Online Admin Center, aka "Microsoft Outlook Information Disclosure Vulnerability." This affects Office 365 ProPlus, Microsoft Office. This CVE ID is unique from CVE-2018-8579.
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Analysis
by VulDB Data Team • 06/06/2023
The CVE-2018-8558 vulnerability represents a significant information disclosure flaw in Microsoft Outlook that undermines the security configuration controls established through SharePoint Online administration. This weakness specifically manifests when Outlook applications fail to properly enforce the "Default link type" settings that administrators configure through the SharePoint Online Admin Center, creating an unexpected data exposure channel that bypasses intended security boundaries. The vulnerability affects Microsoft Office 365 ProPlus and standard Microsoft Office installations, making it particularly concerning given the widespread deployment of these applications across enterprise environments. The flaw operates at the intersection of client-side application behavior and cloud-based administrative controls, demonstrating how misconfigurations in one domain can create unintended access paths in another.
The technical mechanism underlying this vulnerability involves Outlook's improper handling of link type configurations that should normally be enforced by SharePoint Online administrative settings. When administrators configure specific link types through the SharePoint Online Admin Center, these settings are intended to control how external links are treated within the Outlook environment. However, Outlook fails to respect these administrative decisions, allowing users to access content through unauthorized pathways. This behavior creates a situation where sensitive information that should be restricted based on link type configurations becomes accessible to users who would otherwise be prevented from accessing such resources. The vulnerability essentially allows for privilege escalation through information disclosure, where normal access controls are bypassed due to the client application's failure to enforce server-side administrative policies.
The operational impact of CVE-2018-8558 extends beyond simple data exposure to encompass potential compromise of enterprise information security postures. Organizations relying on SharePoint Online's administrative controls for access management may experience unauthorized data access when users interact with links that should be restricted based on the configured default link types. This vulnerability particularly affects scenarios where sensitive documents or resources are shared through SharePoint integration with Outlook, creating potential pathways for information leakage to unauthorized personnel. The risk is compounded in environments where granular access controls are critical for compliance requirements, as the vulnerability undermines the administrative controls that organizations depend upon for maintaining information security boundaries. Security teams may find that their existing SharePoint-based access control configurations become ineffective when users can bypass these restrictions through Outlook client behavior.
Mitigation strategies for this vulnerability should focus on immediate administrative actions and application configuration adjustments. Organizations should first verify that their current SharePoint Online administrative settings are properly configured and understand the scope of affected Outlook installations. Microsoft recommends applying the relevant security updates and patches as soon as they become available to address the underlying implementation flaw. Network administrators should consider implementing additional monitoring controls to detect unusual access patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-200, which addresses "Information Exposure," and can be mapped to ATT&CK technique T1071.004 for application layer protocols and T1068 for local privilege escalation through information disclosure. Organizations should also review their existing access control policies and consider implementing additional security measures such as conditional access policies in Azure Active Directory to provide layered protection against potential exploitation of this information disclosure vulnerability.