Multiple Vulnerabilities in Microsoft Exchange Server Could Allow for Remote Code Execution

Multiple vulnerabilities have been discovered in Microsoft Exchange Server, the most severe of which could allow for remote code execution. Microsoft Exchange Server is a mail server used to run and manage an organizations email services. Successful exploitation of the most severe of these vulnerabilities could allow for remote code execution in the context of the affected service account. Depending on the privileges associated with the account an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Service accounts that are configured to have fewer user rights on the system could be less impacted than those that operate with administrative user rights.

There are multiple reports detailing the active exploitation of these vulnerabilities. GTSC, the Vietnamese cybersecurity company that discovered the two vulnerabilities, reported that they were exploited in early August 2022. According to the GTSC report, cyber threat actors (CTAs) are chaining the vulnerabilities to create backdoors for persistence or to move laterally in the victim network. For example, CTAs exploiting these vulnerabilities deployed the China Chopper webshell for persistent remote access. Some security researchers are referring to the exploit chain as “ProxyNotShell.”

Researchers have warned that Microsoft's mitigation can be bypassed. Security researcher Jang documented how a potential attacker could bypass the proposed mitigation with little effort, and researchers at GTSC confirmed the bypass. Researchers have also warned that users with a hybrid setup combining on-premises and cloud deployment of exchange are also vulnerable to these zero days.

A BleepingComputer report noted that a scammer set up a GitHub repository and is “impersonating security researchers to sell fake proof-of-concept ProxyNotShell exploits” for Exchange CVE-2022-41040 and CVE-2022-41082 vulnerabilities.

CISA is aware of the vulnerabilities and encourages users and administrators to review information from Microsoft and “apply the necessary mitigations until patches are made available.

Multiple vulnerabilities have been discovered in Microsoft Exchange Server, the most severe of which could allow for remote code execution. Details of these vulnerabilities are as follows:
Tactic: Lateral Movement (TA0008):
Technique: Exploitation of Remote Services (T1210):

• CVE-2022-41040 – Microsoft Exchange Server Server-Side Request Forgery (SSRF) vulnerability
• CVE-2022-41082 – Microsoft Exchange Server Remote Code execution vulnerability

In order to successfully exploit the SSRF vulnerability CVE-2022-41040, authentication to the exchange server is required. If CVE-2022-41040 is successfully exploited, it may be chained with CVE-2022-41082 to allow for remote code execution by accessing the PowerShell Remoting Service (default ports 5985/TCP and 5986/TCP).

Successful exploitation of the most severe of these vulnerabilities could allow for remote code execution in the context of the affected service account. Depending on the privileges associated with the account an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Service accounts that are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights.

We recommend the following actions be taken:

• Apply the workarounds provided by Microsoft (link below) until a patch is available. When available, apply appropriate updates provided by Microsoft to vulnerable systems immediately after appropriate testing. (M1051: Update Software)
• Safeguard 7.1: Establish and Maintain a Vulnerability Management Process: Establish and maintain a documented vulnerability management process for enterprise assets. Review and update documentation annually, or when significant enterprise changes occur that could impact this Safeguard.
• Safeguard 7.4: Perform Automated Application Patch Management: Perform application updates on enterprise assets through automated patch management on a monthly, or more frequent, basis.
• Apply the Principle of Least Privilege to all systems and services. Run all software as a non-privileged user (one without administrative privileges) to diminish the effects of a successful attack. (M1026: Privileged Account Management)
• Safeguard 4.7: Manage Default Accounts on Enterprise Assets and Software: Manage default accounts on enterprise assets and software, such as root, administrator, and other pre-configured vendor accounts. Example implementations can include: disabling default accounts or making them unusable.
• Safeguard 5.4: Restrict Administrator Privileges to Dedicated Administrator Accounts: Restrict administrator privileges to dedicated administrator accounts on enterprise assets. Conduct general computing activities, such as internet browsing, email, and productivity suite use, from the user’s primary, non-privileged account.
• Safeguard 5.5: Establish and Maintain an Inventory of Service Accounts: Establish and maintain an inventory of service accounts. The inventory, at a minimum, must contain department owner, review date, and purpose. Perform service account reviews to validate that all active accounts are authorized, on a recurring schedule at a minimum quarterly, or more frequently.
• Safeguard 6.8: Define and Maintain Role-Based Access Control: Define and maintain role-based access control, through determining and documenting the access rights necessary for each role within the enterprise to successfully carry out its assigned duties. Perform access control reviews of enterprise assets to validate that all privileges are authorized, on a recurring schedule at a minimum annually, or more frequently.
• Use capabilities to detect and block conditions that may lead to or be indicative of a software exploit occurring. (M1050: Exploit Protection)
• Safeguard 10.5: Enable Anti-Exploitation Features: Enable anti-exploitation features on enterprise assets and software, where possible, such as Microsoft® Data Execution Prevention (DEP), Windows® Defender Exploit Guard (WDEG), or Apple® System Integrity Protection (SIP) and Gatekeeper™.
• Safeguard 13.10: Performing Application Layer Filtering: Perform application layer filtering. Example implementations include a filtering proxy, application layer firewall, or gateway.