What is CVE-2021-40940?

CVE-2021-40940 is a critical-severity vulnerability in Monstra, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 9.8/10. Published 2022-06-15.

How severe is CVE-2021-40940?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2021-40940 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Arbitrary file upload in Monstra

CVE-2021-40940

Monstra 3.0.4 does not filter the case of php, which leads to an unrestricted file upload vulnerability.

Vulnerability class: Unrestricted File Upload

Published 2022-06-15 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.016 (75.5th percentile), scored 2026-10-08.

Low probability of exploitation in the next 30 days, but still tracked. 76th percentile — 75.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: 0.000

Affected products

Monstra

Weakness classification (CWE)

CWE-434 — Unrestricted Upload of File with Dangerous Type

Public proof-of-concept exploits

References

github.com/monstra-cms/monstra/issues/471 (Exploit, Patch, Third Party Advisory, Issue Tracking)

Frequently asked questions

What is CVE-2021-40940?: CVE-2021-40940 is a critical-severity vulnerability in Monstra, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 9.8/10. Published 2022-06-15.
How severe is CVE-2021-40940?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2021-40940 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.