CVE-2026-1979 is a use-after-free vulnerability found in the mruby interpreter, specifically in the mrb_vm_exec function within the src/vm.c file. The issue arises from the JMPNOT-to-JMPIF optimization logic, where improper handling of memory leads to a use-after-free condition. This vulnerability affects all mruby versions up to and including 3.4.0. Exploitation requires local access with limited privileges but does not require user interaction, making it feasible for an attacker who has already gained some foothold on the system. The use-after-free can cause memory corruption, which may be leveraged to execute arbitrary code, cause a denial of service, or leak sensitive information depending on the context. Although no known exploits are currently observed in the wild, a proof-of-concept exploit has been published, increasing the risk of exploitation. The vulnerability has been assigned a CVSS 4.8 (medium) score, reflecting the local attack vector and limited privileges required. The patch addressing this issue is identified by commit e50f15c1c6e131fa7934355eb02b8173b13df415 and should be applied to affected versions. Organizations using mruby in embedded systems, automation scripts, or custom applications should prioritize patching to prevent potential exploitation.

For European organizations, the impact of CVE-2026-1979 depends on the extent to which mruby is integrated into their software environments. Since mruby is a lightweight Ruby interpreter often embedded in applications or devices, exploitation could lead to local privilege escalation, arbitrary code execution, or denial of service. This can compromise system integrity and availability, especially in critical infrastructure or industrial control systems using mruby. Confidentiality could also be at risk if memory corruption leads to data leakage. The requirement for local access limits remote exploitation, but insider threats or attackers who have already breached perimeter defenses could leverage this vulnerability to deepen their control. Industries such as manufacturing, telecommunications, and software development that embed mruby in their products or internal tools are particularly at risk. Failure to patch could lead to operational disruptions, data breaches, or compromised systems, impacting business continuity and regulatory compliance under GDPR and other European frameworks.

1. Apply the official patch identified by commit e50f15c1c6e131fa7934355eb02b8173b13df415 immediately to all affected mruby versions (3.0 through 3.4.0). 2. Restrict local access to systems running mruby, enforcing strict user privilege separation and monitoring for unauthorized local logins. 3. Implement application whitelisting and integrity monitoring to detect anomalous behavior or exploitation attempts targeting mruby processes. 4. Conduct code audits and dependency reviews to identify where mruby is embedded within organizational software and ensure all instances are updated. 5. Employ endpoint detection and response (EDR) solutions to monitor for suspicious memory corruption or exploitation behaviors locally. 6. Educate internal teams about the risk of local exploitation and enforce strong internal access controls to reduce insider threat risks. 7. Regularly review and update incident response plans to include scenarios involving local exploitation of interpreter vulnerabilities.