CVE-2023-35311 in Outlook
Summary
by MITRE • 07/11/2023
Microsoft Outlook Security Feature Bypass Vulnerability
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Analysis
by VulDB Data Team • 04/25/2025
This vulnerability represents a critical security flaw in Microsoft Outlook that allows attackers to bypass intended security controls designed to protect users from malicious content. The issue stems from how Outlook handles certain email parsing operations and validation mechanisms, creating potential pathways for threat actors to circumvent protection measures. Such vulnerabilities are particularly concerning in enterprise environments where Outlook serves as the primary email client for thousands of users. The flaw typically manifests when Outlook processes specific email headers or attachments that contain crafted malicious content designed to exploit the security bypass mechanism.
The technical implementation of this vulnerability involves manipulation of email processing routines within Outlook's core components, specifically targeting the way the application validates incoming messages and their associated metadata. Attackers can craft emails with carefully constructed elements that trigger unexpected behavior in Outlook's security subsystems. This often involves exploiting weaknesses in input validation, improper handling of special characters, or flawed interpretation of email protocols that should normally be rejected by security filters. The vulnerability may leverage techniques such as header injection, content encoding bypasses, or protocol violation exploitation to achieve the desired bypass effect.
The operational impact of this security flaw extends beyond simple message processing failures and can enable more serious attacks including phishing campaigns, malware delivery, or privilege escalation attempts. When successfully exploited, the vulnerability allows attackers to deliver malicious payloads that would normally be blocked by Outlook's security features, potentially leading to data breaches, system compromise, or further lateral movement within networks. Organizations relying on Outlook for email security may experience significant exposure as threat actors can bypass protection mechanisms designed to prevent known attack patterns and malicious content delivery methods.
Mitigation strategies for this vulnerability typically involve immediate application of Microsoft security patches and updates that address the specific flaw in Outlook's processing logic. Security administrators should also implement additional layers of protection including enhanced email filtering solutions, network-based detection systems, and user awareness training programs. Organizations may need to consider temporary restrictions on certain email protocols or content types until full patches are deployed. The vulnerability demonstrates the importance of maintaining up-to-date security controls and highlights how even well-established applications can contain critical flaws that require rapid response and remediation efforts.
This type of security bypass vulnerability aligns with CWE-1235 which addresses "Security Bypass by Manipulating State" and may also relate to ATT&CK technique T1566 for "Phishing" and T1078 for "Valid Accounts". The vulnerability underscores the need for comprehensive security testing of email clients and highlights how complex applications with extensive feature sets can contain unexpected security gaps. Organizations should regularly review their email security configurations and ensure that multiple defense-in-depth layers are maintained to protect against similar bypass scenarios.