CVE-2026-1979 mruby JMPNOT-to-JMPIF Optimization vm.c mrb_vm_exec use after free

Medium 4.8 Published 6 Feb 2026 Updated 23 Feb 2026

A local attacker can exploit a use-after-free flaw in mruby's VM execution to potentially achieve code execution or privilege escalation.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-1979?

CVE-2026-1979 is a medium-severity use after free vulnerability in mruby, published on 6 Feb 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

A flaw has been found in mruby up to 3.4.0. This affects the function mrb_vm_exec of the file src/vm.c of the component JMPNOT-to-JMPIF Optimization. Executing a manipulation can lead to use after free. The attack needs to be launched locally. The exploit has been published and may be used. This patch is called e50f15c1c6e131fa7934355eb02b8173b13df415. It is advisable to implement a patch to correct this issue.

Weakness: CWE-416, CWE-119

Which versions are affected by CVE-2026-1979?

It affects 1 product.

Products include Mruby Mruby.

How do I fix CVE-2026-1979?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2026-1979 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-1979 exists.

Sources

Also known as DEBIAN-CVE-2026-1979, GHSA-gxgq-rpmr-r8xr, UBUNTU-CVE-2026-1979.