Multiple Vulnerabilities in Rsync Could Allow for Remote Code Execution

Multiple vulnerabilities have been discovered in Rsync, the most severe of which could allow for remote code execution. Rsync is an open-source file synchronization and data transferring tool valued for its ability to perform incremental transfers, reducing data transfer times and bandwidth usage. The tool is utilized extensively by backup systems like Rclone, DeltaCopy, ChronoSync, public file distribution repositories, and cloud and server management operations. Successful exploitation of the most severe of these vulnerabilities could allow for remote code execution in the context of the system. Depending on the privileges associated with the system, an attacker could then install programs; view, change, or delete data. 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.

The CERT Coordination Center (CERT/CC) issued a bulletin warning about the Rsync flaws, marking Red Hat, Arch, Gentoo, Ubuntu NixOS, AlmaLinux OS Foundation, and the Triton Data Center as impacted.

Multiple vulnerabilities have been discovered in Rsync, the most severe of which could allow for remote code execution. Details of these vulnerabilities are as follows:

Tactic: Initial Access (TA0001):

Technique: Exploit Public-Facing Application (T1190):

• Heap Buffer Overflow vulnerability arising from improper handling of checksum lengths in the Rsync daemon, leading to out-of-bounds writes in the buffer. (CVE-2024-12084)
• Information Leak via Uninitialized Stack flaw could allow for the leakage of uninitialized stack data when comparing file checksums. Attackers can manipulate checksum lengths to exploit this vulnerability. (CVE-2024-12085))
• Server Leaks Arbitrary Client Files vulnerability which could allow a malicious server to enumerate and reconstruct arbitrary client files byte-by-byte using manipulated checksum values during file transfer. (CVE-2024-12086)
• Path Traversal via --inc-recursive Option issue that stems from inadequate symlink verification when using the --inc-recursive option. Malicious servers can write files outside the intended directories on the client. (CVE-2024-12087)
• Bypass of --safe-links Option flow occurs when Rsync fails to properly verify symbolic link destinations containing other links. It results in path traversal and arbitrary file writes outside designated directories. (CVE-2024-12088)
• Symbolic Link Race Condition vulnerability arising from a race condition in handling symbolic links. Exploitation may allow attackers to access sensitive files and escalate privileges. (CVE-2024-12747)

Successful exploitation of the most severe of these vulnerabilities could allow for remote code execution in the context of the system. Depending on the privileges associated with the system, an attacker could then install programs; view, change, or delete data.

We recommend the following actions be taken:

• Apply appropriate updates provided by Openwall 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 7.2: Establish and Maintain a Remediation Process: Establish and maintain a risk-based remediation strategy documented in a remediation process, with monthly, or more frequent, reviews.
• 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 7.5 : Perform Automated Vulnerability Scans of Internal Enterprise Assets: Perform automated vulnerability scans of internal enterprise assets on a quarterly, or more frequent, basis. Conduct both authenticated and unauthenticated scans, using a SCAP-compliant vulnerability scanning tool.
• 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 12.1: Ensure Network Infrastructure is Up-to-Date: Ensure network infrastructure is kept up-to-date. Example implementations include running the latest stable release of software and/or using currently supported network-as-a-service (NaaS) offerings. Review software versions monthly, or more frequently, to verify software support.
• Safeguard 18.1: Establish and Maintain a Penetration Testing Program: Establish and maintain a penetration testing program appropriate to the size, complexity, and maturity of the enterprise. Penetration testing program characteristics include scope, such as network, web application, Application Programming Interface (API), hosted services, and physical premise controls; frequency; limitations, such as acceptable hours, and excluded attack types; point of contact information; remediation, such as how findings will be routed internally; and retrospective requirements.
• Safeguard 18.2: Perform Periodic External Penetration Tests: Perform periodic external penetration tests based on program requirements, no less than annually. External penetration testing must include enterprise and environmental reconnaissance to detect exploitable information. Penetration testing requires specialized skills and experience and must be conducted through a qualified party. The testing may be clear box or opaque box.
• Safeguard 18.3: Remediate Penetration Test Findings: Remediate penetration test findings based on the enterprise’s policy for remediation scope and prioritization.

• 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 5.5: 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.

• Vulnerability scanning is used to find potentially exploitable software vulnerabilities to remediate them. (M1016: Vulnerability Scanning)
• Safeguard 16.13: Conduct Application Penetration Testing: Conduct application penetration testing. For critical applications, authenticated penetration testing is better suited to finding business logic vulnerabilities than code scanning and automated security testing. Penetration testing relies on the skill of the tester to manually manipulate an application as an authenticated and unauthenticated user.

• Architect sections of the network to isolate critical systems, functions, or resources. Use physical and logical segmentation to prevent access to potentially sensitive systems and information. Use a DMZ to contain any internet-facing services that should not be exposed from the internal network. Configure separate virtual private cloud (VPC) instances to isolate critical cloud systems. (M1030: Network Segmentation)
• Safeguard 12.2: Establish and Maintain a Secure Network Architecture: Establish and maintain a secure network architecture. A secure network architecture must address segmentation, least privilege, and availability, at a minimum.

• 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™.