How severe is CVE-2021-40940?

CVE-2021-40940 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-40940 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40940?

CVE-2021-40940 affects Monstra. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40940?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-40940 published?

CVE-2021-40940 was published on 2022-06-15 and last updated on 2026-06-17.

CVE-2021-40940

CVE-2021-40940 is a critical-severity vulnerability in Monstra with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-434.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 2% (75th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-434
Affected product: Monstra
Published: 2022-06-15
Last modified: 2026-06-17

Description

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

Frequently asked questions

What is CVE-2021-40940?: Monstra 3.0.4 does not filter the case of php, which leads to an unrestricted file upload vulnerability.
How severe is CVE-2021-40940?: CVE-2021-40940 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-40940 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40940?: CVE-2021-40940 affects Monstra. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40940?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-40940 published?: CVE-2021-40940 was published on 2022-06-15 and last updated on 2026-06-17.

References

https://github.com/monstra-cms/monstra/issues/471

Affected products (1)

cpe:2.3:a:monstra:monstra:*:*:*:*:*:*:*:*

More vulnerabilities in Monstra

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CVE-2018-6383 — High (CVSS 8.8): Monstra CMS through 3.0.4 has an incomplete "forbidden types" list that excludes .php (and similar) file extensions but…

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Other CWE-434 (Unrestricted Upload of File with Dangerous Type) vulnerabilities

CVE-2026-39770 — Critical (CVSS 10.0): Unauthenticated Arbitrary File Upload in Doctreat <= 1.7.0 versions.
CVE-2026-32579 — Critical (CVSS 10.0): Unauthenticated Arbitrary File Upload in Kognetiks Chatbot for WordPress <= 2.4.9 versions.
CVE-2026-102427 — Critical (CVSS 10.0): Joomla Extension - ordasoft.com - Unauthenticated Remote Code Execution in OrdaSoft Joomla CCK < 8.3.16 -…
CVE-2026-4357 — Critical (CVSS 10.0): The Embed HTML5 Game WordPress plugin through 1.3 does not properly restrict who can upload files via the plugin, as…
CVE-2026-84147 — Critical (CVSS 10.0): This vulnerability exists in the ERP system due to improper authentication controls and inadequate file type validation…
CVE-2026-81780 — Critical (CVSS 10.0): Unauthenticated Arbitrary File Upload in Hash Form <= 1.4.2 versions.

Browse all CWE-434 (Unrestricted Upload of File with Dangerous Type) vulnerabilities →