CVE-2019-0858 in Exchange Server
Summary
by MITRE
A spoofing vulnerability exists in Microsoft Exchange Server when Outlook Web Access (OWA) fails to properly handle web requests, aka 'Microsoft Exchange Spoofing Vulnerability'. This CVE ID is unique from CVE-2019-0817.
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Analysis
by VulDB Data Team • 05/28/2020
The vulnerability described in CVE-2019-0858 represents a critical spoofing weakness within Microsoft Exchange Server's Outlook Web Access component that enables attackers to manipulate web request handling processes. This security flaw specifically affects the authentication and validation mechanisms employed by OWA, creating opportunities for malicious actors to exploit the system's trust model and potentially gain unauthorized access to email accounts. The vulnerability stems from insufficient validation of web requests that traverse through the Exchange Server infrastructure, particularly when users interact with the web-based email interface.
The technical implementation of this vulnerability resides in the improper handling of HTTP requests within the Exchange Server's web processing pipeline. When Outlook Web Access processes incoming web requests, it fails to adequately validate or sanitize the request parameters, allowing attackers to craft malicious requests that can bypass normal authentication checks. This weakness creates a pathway for attackers to manipulate session tokens, user identifiers, or other critical request components that should normally be validated by the system. The flaw operates at the application layer of the OSI model, specifically within the web application processing logic that handles user authentication and authorization. According to CWE-346, this vulnerability aligns with improper validation of data flow, where the system fails to properly validate that incoming data conforms to expected formats and security parameters.
The operational impact of this vulnerability extends beyond simple spoofing capabilities, potentially enabling attackers to perform session hijacking, unauthorized email access, and privilege escalation within the Exchange environment. An attacker could exploit this weakness to impersonate legitimate users, access sensitive email communications, or manipulate email routing and delivery processes. The vulnerability particularly affects organizations that rely heavily on web-based email access through Outlook Web Access, as it directly undermines the security assurances provided by the Exchange Server authentication system. The attack surface is significant given that OWA is a commonly used interface for remote email access, making this vulnerability particularly attractive to threat actors seeking persistent access to corporate email systems.
Organizations affected by CVE-2019-0858 should implement immediate mitigations including applying the relevant Microsoft security updates and patches that address the web request handling logic within Exchange Server. Network segmentation and monitoring of OWA traffic can help detect anomalous request patterns that may indicate exploitation attempts. The vulnerability also aligns with tactics described in the MITRE ATT&CK framework under initial access and credential access phases, where attackers may leverage spoofing capabilities to establish footholds within target environments. Additionally, implementing multi-factor authentication and strengthening authentication mechanisms can provide additional defense layers against exploitation attempts. Security teams should conduct thorough assessments of their Exchange Server configurations and review web application logs for signs of unauthorized access attempts that may indicate exploitation of this vulnerability.