---
id: CVE-2026-86547
title: >-
  mrubyc through 4.0.0 contains a null pointer dereference vulnerability in the
  op_enter() handler in src/vm.c when processing untrusted bytecode
summary: >-
  mrubyc through 4.0.0 contains a null pointer dereference vulnerability in the
  op_enter() handler in src/vm.c when processing untrusted bytecode. Attackers
  can craft malicious .mrb bytecode files with OP_ENTER instructions at the top
  leve…
severity: medium
cvss: 6.2
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-476
vendor: mrubyc
product: mrubyc
affected:
  - mrubyc >= 2.0 <= 4.0.0
published: '2026-09-09'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T19:58:20.507'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-86547'
references:
  - url: >-
      https://github.com/mrubyc/mrubyc/blob/4261cf5e5ae5579e3110dab98a04b91c7d919429/src/vm.c#L1534
    label: disclosure@vulncheck.com
  - url: 'https://github.com/mrubyc/mrubyc/blob/release4.0.0/src/vm.c#L1537'
    label: disclosure@vulncheck.com
  - url: >-
      https://www.vulncheck.com/advisories/mrubyc-through-4.0.0-null-pointer-dereference-via-op-enter
    label: disclosure@vulncheck.com
tags:
  - nvd
  - cve.org
  - exploit-available
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-09T12:41:01.119978Z'
ingestedAt: '2026-09-10T14:24:27.789Z'
epss: 0.00184
epssPercentile: 0.07065
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/HarshRajSinghania/cve-2026-86547-mrubyc-op-enter'
  checkedAt: '2026-09-26T09:06:03.528Z'
exploitAvailable: true
---

## Overview

mrubyc through 4.0.0 contains a null pointer dereference vulnerability in the op_enter() handler in src/vm.c when processing untrusted bytecode. Attackers can craft malicious .mrb bytecode files with OP_ENTER instructions at the top level to crash the embedding application and cause denial of service.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.