# CVE-2026-38973: mrubyc out-of-bounds read in mrbc_find_method

Source: https://junglewise.ai/threats/cve-2026-38973-mrubyc-out-of-bounds-read-in-mrbc-find-method  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-06. Updated: 2026-07-06  
License: CC BY 4.0 with a link back

CVE-2026-38973 · Severity: info · CVSS 0 · Published 2026-07-06

mruby/c is a lightweight implementation of the Ruby programming language designed for microcontrollers and embedded systems with very limited memory. A technical flaw in how the software looks up internal functions could allow a specially crafted program to read data from memory locations it should not have access to. This could potentially lead to system instability or the exposure of sensitive information stored in the device's memory.

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

## Quick answers

**Is CVE-2026-38973 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-38973 being exploited in the wild.

**How severe is CVE-2026-38973?** Informational severity, with a CVSS score of 0, published 6 July 2026.

**Which products and versions are affected?** Mrubyc through 3.4.1.

**Is there a fix for CVE-2026-38973?** 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-2026-38973 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-38973?** 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

An out-of-bounds read vulnerability exists in mrubyc through version 3.4.1 within the `mrbc_find_method()` function in `src/class.c`. The issue stems from improper boundary handling during a binary search of builtin method symbols, specifically where the `right` index was not correctly decremented relative to the number of builtin methods. An attacker capable of executing arbitrary Ruby code on the VM could trigger this out-of-bounds read during method lookup. This could result in a crash (denial of service) or information disclosure from the heap. A fix has been identified in commit f83a8b6 which correctly adjusts the search bounds.

## Affected products

- mrubyc mrubyc through 3.4.1

## Timeline

- 2026-07-06: disclosed
- 2026-07-06: advisory

## References

- [https://github.com/mrubyc/mrubyc](https://github.com/mrubyc/mrubyc)
- [https://github.com/mrubyc/mrubyc/commit/f83a8b67ca1c7c62ac0dd548a363d79f767c4e30](https://github.com/mrubyc/mrubyc/commit/f83a8b67ca1c7c62ac0dd548a363d79f767c4e30)
- [https://github.com/mrubyc/mrubyc/issues/279%2C](https://github.com/mrubyc/mrubyc/issues/279%2C)

## Related threats

- [mrubyc null pointer dereference in op_enter handler](https://junglewise.ai/threats/cve-2026-86547-mrubyc-null-pointer-dereference-in-op-enter-handler)
- [mrubyc NULL pointer dereference in op_super](https://junglewise.ai/threats/cve-2026-38976-mrubyc-null-pointer-dereference-in-op-super)