What is CVE-2021-4188?

CVE-2021-4188 is a high-severity vulnerability in Mruby, classified under NULL Pointer Dereference. CVSS score: 7.5/10. Published 2021-12-30.

How severe is CVE-2021-4188?

High severity. CVSS v3 base score is 7.5 out of 10.

NULL pointer dereference in Mruby

CVE-2021-4188

mruby is vulnerable to NULL Pointer Dereference

Published 2021-12-30 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (56.8th percentile), scored 2026-10-01.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 57th percentile — 56.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Mruby
Mruby Mruby/mruby — versions unspecified

Weakness classification (CWE)

CWE-476 — NULL Pointer Dereference

References

huntr.dev/bounties/78533fb9-f3e0-47c2-86dc-d1f96d5bea28 (Exploit, Patch, Third Party Advisory)
github.com/mruby/mruby/commit/27d1e0132a0804581dca28df042e7047fd27eaa8 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-4188?: CVE-2021-4188 is a high-severity vulnerability in Mruby, classified under NULL Pointer Dereference. CVSS score: 7.5/10. Published 2021-12-30.
How severe is CVE-2021-4188?: High severity. CVSS v3 base score is 7.5 out of 10.