# CVE-2026-86547: mrubyc null pointer dereference in op_enter handler

Source: https://junglewise.ai/threats/cve-2026-86547-mrubyc-null-pointer-dereference-in-op-enter-handler  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-09. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-86547 · Severity: medium · CVSS 6.2 · Published 2026-09-09

mrubyc is a lightweight Ruby virtual machine designed for embedded systems and microcontrollers. A null pointer dereference vulnerability allows an attacker to crash applications using mrubyc by providing malicious bytecode files, causing service denial and potential system instability.

Technologies: [Mrubyc](https://junglewise.ai/threats/technologies/mrubyc). Vendors: [Mrubyc](https://junglewise.ai/threats/vendors/mrubyc).

## Quick answers

**Is CVE-2026-86547 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-86547 being exploited in the wild.

**How severe is CVE-2026-86547?** Medium severity, with a CVSS score of 6.2, published 9 September 2026.

**Which products and versions are affected?** Mrubyc through 4.0.0.

**Is there a fix for CVE-2026-86547?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-86547 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-86547?** Check whether you run Mrubyc at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A null pointer dereference vulnerability exists in the op_enter() handler within src/vm.c when processing OP_ENTER instructions in untrusted bytecode. Attackers can craft malicious .mrb bytecode files that place OP_ENTER instructions at the top level (outside of function/method definitions) to trigger the null dereference, crashing the embedding application. The vulnerability is triggered when bytecode is loaded and executed; no authentication or special privileges are required. An attacker can achieve denial of service by causing the application to crash, but code execution is not directly possible from this vulnerability alone.

## Affected products

- mrubyc mrubyc through 4.0.0

## Timeline

- 2026-09-09: disclosed

## References

- [https://github.com/mrubyc/mrubyc](https://github.com/mrubyc/mrubyc)
- [https://github.com/mrubyc/mrubyc/blob/4261cf5e5ae5579e3110dab98a04b91c7d919429/src/vm.c](https://github.com/mrubyc/mrubyc/blob/4261cf5e5ae5579e3110dab98a04b91c7d919429/src/vm.c)

## Related threats

- [mrubyc NULL pointer dereference in op_super](https://junglewise.ai/threats/cve-2026-38976-mrubyc-null-pointer-dereference-in-op-super)
- [mrubyc out-of-bounds read in mrbc_find_method](https://junglewise.ai/threats/cve-2026-38973-mrubyc-out-of-bounds-read-in-mrbc-find-method)