Description
A critical vulnerability has been identified in the Microsoft Outlook email client, designated as CVE-2023-35311, which involves a security feature bypass. This vulnerability poses a significant risk as it allows malicious actors to circumvent critical security checks designed to prevent unauthorized actions.
Affected Product(s)
- Microsoft 365 Apps for Enterprise,
- Microsoft Office 2019
Technical Details
Microsoft Outlook, part of the broader Office and 365 productivity suites, is a widely used email application offering various features such as email communication, calendar scheduling, and task management. The identified vulnerability, CVE-2023-35311, is a security feature bypass issue. This specific vulnerability exists in Microsoft Outlook, where certain security features can be bypassed due to improper input validation and a race condition, potentially allowing an attacker to perform unauthorized actions.
The vulnerability, when exploited, could allow an attacker to bypass security features such as URL validation and execution restrictions. Specifically, the issues are:
- CWE-20: Improper Input Validation โ This occurs when an application does not properly validate inputs that might be modified by an attacker to intentionally bypass security mechanisms or cause the application to execute unintended commands. In the case of Outlook, malformed URLs can be used to bypass safety checks.
- CWE-367: Time-of-Check Time-of-Use (TOCTOU) Race Condition โ This arises when there is a delay between the security check performed by the application and the subsequent use of the result of that check.
An attacker could alter the input before it is used, bypassing the initially perceived safe condition. Malicious users can craft special URLs and inject them into emails sent via Outlook. When the recipient, using a vulnerable version of Outlook, clicks on these URLs, the security measures supposed to detect and block potentially unsafe links fail to function correctly. This allows the attacker to execute further malicious activities such as downloading additional payloads or gaining unauthorized access. The affected configurations include:
- Microsoft 365 Apps for Enterprise for both 32-bit and 64-bit systems.
- Microsoft Office 2019 across various platforms, including Windows x64 and x86, Mac OS, and Mac OS X.
Further technical details reveal that exploitation of this vulnerability requires user interaction, meaning the attacker must convince the user to follow a malicious link or open a harmful email. This method, although requiring some level of social engineering, is highly effective as it leverages the trust users place in emails appearing to be from legitimate sources. Microsoft has acknowledged the severity of this vulnerability and its potential for being exploited, listing it among the risks that need immediate attention and mitigation measures.
The vulnerabilities identified have been addressed in updates provided in the security bulletins, urging users to apply these patches promptly to safeguard their systems. If left unpatched, attackers could exploit these weaknesses relatively straightforwardly to bypass crucial security mechanisms put in place, jeopardizing the integrity and confidentiality of data managed within Microsoft Outlook.
Reference links for further details on how this vulnerability operates and its broader implications include sources such as the National Vulnerability Database, Microsoftโs Security Response Center, and other security advisories.
Comprehensive patches released cover a range of Office versions and configurations, ensuring that users of various Outlook installations can secure their applications effectively by following recommended update paths.
Weakness
The vulnerability is primarily associated with the following weaknesses:
- Improper Input Validation (CWE-20): The application fails to correctly validate all input data, allowing attackers to submit malicious links that bypass existing security checks.
- Time-of-Check Time-of-Use (TOCTOU) Race Condition (CWE-367): The time between the validation of the input and its actual use is exploited by attackers to introduce unauthorized modifications, enabling them to bypass security controls.
Impact Assessment
If exploited, this vulnerability could allow an attacker to gain unauthorized access to sensitive data or execute arbitrary actions on the affected system. Specifically, the potential consequences include:
- Bypassing URL validation and execution restrictions, allowing for the download and installation of additional malicious software.
- Gaining unauthorized access to the system where Outlook is installed, potentially leading to broader network infiltration and data breaches.
- Facilitating other types of attacks, such as phishing or spear-phishing, by exploiting the perceived trust in benign email communications.
The impact is rated as critical due to the widespread use of Microsoft Outlook in both enterprise and personal environments, making it a high-priority target for cyber adversaries.
Active Exploitation
Active exploitation of CVE-2023-35311 has been observed, primarily involving threat actors leveraging the vulnerability to conduct sophisticated phishing attacks and bypass security measures. While specific adversary groups exploiting this vulnerability have not been named, the nature of these exploits aligns with methods used by various known cyber threat groups specializing in email-based attacks and social engineering.
The critical aspect to note is the frequency and persistence of these exploitation attempts, underscoring the importance of applying updates and patches without delay to mitigate the risk effectively.
Ransomware Association
While there have been no specific instances directly linking this vulnerability to ransomware attacks, the potential exists for such attacks to develop. Ransomware operators often exploit security vulnerabilities to gain initial access to target systems, and this security feature bypass provides a viable entry point for such malicious activities. Prevention against these risks necessitates immediate attention to patches and security updates.
Mitigation and Resolution
We have released a patch that addresses this vulnerability. Please update to the latest versions of Microsoft 365 Apps for Enterprise and Microsoft Office 2019 as follows:
- Apply the security updates provided in the Microsoft bulletins for KB5002427 and KB5002432.
- Ensure your systems are configured to automatically receive and apply security updates where possible.
- Follow best practices for email security, including scrutiny of unfamiliar and unexpected emails containing links or attachments.
Continued vigilance and prompt action regarding patches and updates are critical to protecting against exploitation of this security feature bypass.
Recommendations
- We strongly recommend that all customers apply the latest patch as soon as possible.
- Verify that automatic updates are enabled to ensure timely application of future patches.
- Educate users about the risks of clicking on links or opening attachments from unknown or untrusted sources.
- Monitor network and email traffic for signs of unusual activity that may indicate exploitation attempts.
- Implement additional email security measures, such as robust spam and phishing filters.
- Regularly back up critical data to recover quickly in case of a security breach.
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