CVE-2025-13120 is a use-after-free vulnerability discovered in the mruby interpreter, a lightweight Ruby implementation used primarily in embedded systems and applications requiring a small footprint. The flaw exists in the sort_cmp function located in src/array.c, where improper memory management leads to use-after-free conditions. This vulnerability arises when the function manipulates array elements during sorting, freeing memory that is subsequently accessed, resulting in undefined behavior. Exploitation requires local access with low privileges and does not require user interaction, which means an attacker with limited system access can trigger the flaw. The vulnerability can cause memory corruption, leading to application crashes or potentially arbitrary code execution if exploited skillfully. The vulnerability affects mruby versions 3.0 through 3.4.0. A patch has been released (commit eb398971bfb43c38db3e04528b68ac9a7ce509bc) to correct the issue. The CVSS 4.0 vector assigns a score of 4.8 (medium severity), reflecting the local attack vector, low complexity, no user interaction, and limited scope. No known exploits are currently observed in the wild, but public disclosure increases the risk of exploitation attempts. Organizations using mruby in development environments, embedded devices, or custom applications should prioritize patching to mitigate potential risks.

For European organizations, the impact of CVE-2025-13120 depends largely on the extent of mruby usage within their environments. Since mruby is often embedded in IoT devices, industrial control systems, or used in lightweight scripting contexts, exploitation could lead to denial of service or unauthorized code execution on affected devices. This could disrupt operations, especially in sectors like manufacturing, telecommunications, and critical infrastructure where embedded Ruby interpreters are integrated. Confidentiality risks are moderate, as local access is required, but integrity and availability could be compromised if attackers leverage the vulnerability to execute arbitrary code or cause system crashes. The medium CVSS score reflects these constraints. European organizations with development teams using mruby for testing or internal tools may also face risks if attackers gain local access to developer machines. Overall, the threat is significant for environments where mruby is deployed on devices or systems with sensitive operational roles or limited physical security.

1. Immediately apply the official patch identified by commit eb398971bfb43c38db3e04528b68ac9a7ce509bc to all affected mruby versions (3.0 through 3.4.0). 2. Conduct an inventory of all systems and devices running mruby to identify exposure, including embedded devices and development environments. 3. Restrict local access to systems running mruby to trusted users only, employing strong authentication and access controls to reduce the risk of local exploitation. 4. Implement monitoring for unusual process crashes or memory corruption symptoms that could indicate exploitation attempts. 5. For embedded devices, ensure secure firmware update mechanisms are in place to deploy patches efficiently. 6. Educate developers and system administrators about the vulnerability and the importance of applying updates promptly. 7. Where possible, isolate systems running mruby from critical networks to limit potential lateral movement in case of compromise. 8. Review and harden system configurations to minimize privilege levels and reduce the attack surface around mruby usage.