Heap-buffer-overflow in mrb_funcall_with_block in mruby

mruby Updated 02 Oct 2025

Summary

15/10/2021

Disclosed on

HIGH

Severity

Yes i

Fix available

High

Severity

Not published

CVSS Score

OSV-2021-1455: Heap-buffer-overflow in mrb_funcall_with_block. Affects mruby versions >= dccd66f9efecd0a974b735c62836fe566015cf37, < 7010ed0f0a414b1367e4620a504f106759341cc2. Fixed in 7010ed0f0a414b1367e4620a504f106759341cc2. How to fix ↓

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Background

mruby is an open-source lightweight implementation of the Ruby programming language. It is designed to be embedded in other applications and provides a minimalistic and efficient runtime environment. The mrb_funcall_with_block function in mruby is responsible for calling a Ruby method with a block. This vulnerability in mruby allows for a heap-buffer-overflow WRITE of 8 bytes. The issue was reported through the OSS-Fuzz project and can lead to crashes in the mrb_funcall_with_block function, specifically when mrb_funcall_argv and const_get are invoked.

Vulnerability Detail

The vulnerability arises from a heap-buffer-overflow WRITE of 8 bytes in the mrb_funcall_with_block function. This can potentially lead to crashes and may be exploitable to execute arbitrary code or cause denial of service. The issue was discovered through the OSS-Fuzz project, which identified the crash state as mrb_funcall_with_block, mrb_funcall_argv, and const_get. The severity of this vulnerability is classified as HIGH.

How To Fix

Minimum fixed version

7010ed0f0a414b1367e4620a504f106759341cc2

This is the first release that contains the fix.

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Workaround

As a workaround, if updating the mruby package is not immediately feasible, developers can consider implementing input validation and sanitization to prevent triggering the vulnerable code path. Additionally, enabling address sanitization tools during compilation may help detect potential heap-buffer-overflow issues.

Conclusion

In conclusion, the mrb_funcall_with_block function in mruby is vulnerable to a heap-buffer-overflow WRITE of 8 bytes. This can potentially lead to crashes and may be exploitable to execute arbitrary code or cause denial of service. It is recommended to update the mruby package to a version that includes the fix. For further support on vulnerability remediation, please contact DevNack.com.

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