CVE-2025-13120 is a use-after-free vulnerability discovered in the mruby interpreter, a lightweight Ruby implementation commonly embedded in applications and devices. The vulnerability resides in the sort_cmp function of the src/array.c file, where improper memory management leads to a use-after-free condition. This occurs when the function manipulates array elements during sorting, freeing memory that is still referenced afterward, causing undefined behavior. Exploitation requires local access with low privileges and no user interaction, indicating that an attacker must have some level of access to the target system to trigger the flaw. The vulnerability affects all mruby versions up to and including 3.4.0. The disclosed patch (commit eb398971bfb43c38db3e04528b68ac9a7ce509bc) corrects the issue by properly managing memory during the sort operation. While no public exploits are known to be actively used, the public disclosure increases the risk of exploitation attempts. The CVSS v4.0 base score is 4.8, reflecting medium severity due to the local attack vector, low complexity, and potential impact on confidentiality, integrity, and availability. This vulnerability could be leveraged to execute arbitrary code, cause application crashes, or escalate privileges within the local environment.

The primary impact of CVE-2025-13120 is the potential for local attackers to exploit the use-after-free vulnerability to corrupt memory, leading to application crashes, denial of service, or possibly arbitrary code execution within the context of the mruby interpreter. This can compromise the confidentiality, integrity, and availability of applications embedding mruby, especially if they run with elevated privileges or handle sensitive data. Systems relying on mruby for scripting or automation could be destabilized or manipulated, affecting business operations and security. Although remote exploitation is not feasible, insider threats or attackers with local access could leverage this flaw to escalate privileges or disrupt services. The medium CVSS score reflects a moderate risk, but the real-world impact depends on the deployment context and the privileges of the mruby process. Organizations using mruby in critical infrastructure, embedded devices, or development environments may face increased risk of targeted attacks or system instability if unpatched.

To mitigate CVE-2025-13120, organizations should promptly apply the official patch identified by commit eb398971bfb43c38db3e04528b68ac9a7ce509bc to all affected mruby versions up to 3.4.0. If immediate patching is not feasible, consider restricting local access to systems running mruby to trusted users only, minimizing the attack surface. Employ application whitelisting and monitoring to detect unusual behavior in processes using mruby. Conduct thorough code reviews and testing when embedding mruby in custom applications to identify potential misuse of the sort_cmp function or similar array operations. Additionally, implement least privilege principles for processes running mruby to limit the impact of potential exploitation. Regularly update and audit all dependencies, including mruby, to ensure timely application of security fixes. Finally, maintain robust logging and alerting mechanisms to detect exploitation attempts or crashes related to this vulnerability.