MS-ISAC CYBERSECURITY ADVISORY
MS-ISAC ADVISORY NUMBER:
A Vulnerability in KSMBD for Linux Could Allow for Remote Code Execution
A vulnerability have been discovered in KSMBD for Linux that could allow for remote code execution. KSMBD is a Linux kernel daemon which implements SMB3 protocol in kernel space for sharing files over network. Successful exploitation of this vulnerability could allow for arbitrary code execution in the context of a remote unauthenticated user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts are configured to have fewer user rights on the system could be less impacted than those who operate with administrative user rights.
Linux is un-aware that an exploit for CVE-2022-47939 exists in the wild.
- KSMBD for Linux as installed on Linux kernel versions 5.15 through 5.19 before 5.19.2
- RedHat has confirmed there products are not affected.
- Ubuntu/Debian has confirmed there are some affected products but exploitation requires KSMBD to be enabled, which requires ksmbd-tools to be installed, which is not by default
- Large and medium government entities: Medium
- Small government entities: Medium
- Large and medium business entities: Medium
- Small business entities: Medium
Home users: Low
A vulnerability has been discovered in KSMBD for Linux that could allow for remote code execution. Details of the vulnerabilities are as follows:
Tactic: Execution (TA0002):
Technique: Command and Scripting Interpreter: Unix Shell (T1059.004):
- This vulnerability allows remote attackers to execute arbitrary code on affected installations of Linux Kernel. Authentication is not required to exploit this vulnerability, but only systems with ksmbd enabled are vulnerable. The specific flaw exists within the processing of SMB2_TREE_DISCONNECT commands. The issue results from the lack of validating the existence of an object prior to performing operations on the object. An attacker can leverage this vulnerability to execute code in the context of the kernel. (CVE-2022-47939)
Successful exploitation of this vulnerability could allow for arbitrary code execution in the context of a remote unauthenticated user. Depending on the privileges associated with the user, an attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. Users whose accounts 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:
- Block execution of code on a system through application control, and/or script blocking. (M1038: Execution Prevention)
- Safeguard 2.5: Use technical controls, such as application allowlisting, to ensure that only authorized software can execute or be accessed.
- Safeguard 2.7: Use technical controls, such as digital signatures and version control, to ensure that only authorized scripts, such as specific .ps1, .py, etc., files are allowed to execute. Block unauthorized scripts from executing.
- Apply appropriate updates provided by Linux 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.
- Safeguard 7.7: Remediate Detected Vulnerabilities: Remediate detected vulnerabilities in software through processes and tooling on a monthly, or more frequent, basis, based on the remediation process.
- Safeguard 9.1: Ensure Use of Only Fully Supported Browsers and Email Clients: Ensure only fully supported browsers and email clients are allowed to execute in the enterprise, only using the latest version of browsers and email clients provided through the vendor.
- 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.
- Restrict execution of code to a virtual environment on or in transit to an endpoint system. (M1048: Application Isolation and Sandboxing)
- Safeguard 4.1: Establish and Maintain a Secure Configuration Process: Establish and maintain a secure configuration process for enterprise assets (end-user devices, including portable and mobile, non-computing/IoT devices, and servers) and software (operating systems and applications). Review and update documentation annually, or when significant enterprise changes occur that could impact this Safeguard.
- Safeguard 16.8: Separate Production and Non-Production Systems: Maintain separate environments for production and non-production systems.
- 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.
- Safeguard 9.2: Use DNS Filtering Services: Use DNS filtering services on all enterprise assets to block access to known malicious domains.
- Safeguard 9.3: Maintain and Enforce Network-Based URL Filters: Enforce and update network-based URL filters to limit an enterprise asset from connecting to potentially malicious or unapproved websites. Example implementations include category-based filtering, reputation-based filtering, or through the use of block lists. Enforce filters for all enterprise assets.
- Safeguard 9.6: Block Unnecessary File Types: Block unnecessary file types attempting to enter the enterprise’s email gateway.
- Inform and educate users regarding the threats posed by hypertext links contained in emails or attachments especially from un-trusted sources. Remind users not to visit un-trusted websites or follow links provided by unknown or un-trusted sources. (M1017: User Training)
- Safeguard 14.1: Establish and Maintain a Security Awareness Program: Establish and maintain a security awareness program. The purpose of a security awareness program is to educate the enterprise’s workforce on how to interact with enterprise assets and data in a secure manner. Conduct training at hire and, at a minimum, annually. Review and update content annually, or when significant enterprise changes occur that could impact this Safeguard.
- Safeguard 14.2: Train Workforce Members to Recognize Social Engineering Attacks: Train workforce members to recognize social engineering attacks, such as phishing, pre-texting, and tailgating.