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

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

- **Severity:** Medium 4.8 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P`)
- **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:** Yes
- **Published:** 6 Feb 2026
- **Updated:** 23 Feb 2026
- **Also known as:** DEBIAN-CVE-2026-1979, GHSA-gxgq-rpmr-r8xr, UBUNTU-CVE-2026-1979

## 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 (Use After Free), CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2026-1979?

It affects 1 product.


Products: Mruby Mruby.

## How do I fix CVE-2026-1979?

Apply the vendor's patch.

## Is CVE-2026-1979 being exploited?

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

## Other vulnerabilities in mruby

- [CVE-2020-6838](https://insights.sbomify.com/CVE-2020-6838/): Use after free in n/a (critical 9.8)
- [CVE-2020-6839](https://insights.sbomify.com/CVE-2020-6839/): Memory corruption in n/a (critical 9.8)
- [CVE-2020-6840](https://insights.sbomify.com/CVE-2020-6840/): Use after free in n/a (critical 9.8)
- [CVE-2018-10199](https://insights.sbomify.com/CVE-2018-10199/): Use after free in n/a (critical 9.8)
- [CVE-2022-1212](https://insights.sbomify.com/CVE-2022-1212/): Use-After-Free in str_escape in mruby/mruby in mruby/mruby (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-1979 and fix it if it is affected.

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

Affected product: mruby. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-1979/ (Markdown: https://insights.sbomify.com/CVE-2026-1979/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-1979
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-1979
- OSV: https://osv.dev/vulnerability/CVE-2026-1979

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-1979/
Summaries are generated and may contain mistakes; the official description above is the record.