What’s Vulnerable › Vulnerabilities

CVE-2021-37334

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 2.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-25 · updated 2026-06-17

Description

Umbraco Forms version 4.0.0 up to and including 8.7.5 and below are vulnerable to a security flaw that could lead to a remote code execution attack and/or arbitrary file deletion. A vulnerability occurs because validation of the file extension is performed after the file has been stored in a temporary directory. By default, files are stored within the application directory structure at %BASEDIR%/APP_DATA/TEMP/FileUploads/. Whilst access to this directory is restricted by the root web.config file, it is possible to override this restriction by uploading another specially crafted web.config file to the temporary directory. It is possible to exploit this flaw to upload a malicious script file to execute arbitrary code and system commands on the server.

Affected products

• umbraco Forms: from 4.0.0 before 4.4.9; from 6.0.0 before 6.0.10; from 7.0.0 before 7.0.7; from 7.1.0 before 7.1.4; from 7.2.0 before 7.2.1; from 7.3.0 before 7.3.2 — fixed in 4.4.9, 6.0.10, 7.0.7, 7.1.4, 7.2.1, 7.3.2

How to fix

Upgrade to a fixed version: umbraco Forms 4.4.9, 6.0.10, 7.0.7, 7.1.4. Check the vendor advisory for mitigations.

References

• https://umbraco.com/blog/security-advisory-20th-of-july-2021-patch-is-now-available/
• https://umbraco.com/blog/security-advisory-security-patches-for-umbraco-forms-ready-on-july-20th-2021-at-7-am-utc/
• https://umbraco.com/blog/security-advisory-20th-of-july-2021-patch-is-now-available/
• https://umbraco.com/blog/security-advisory-security-patches-for-umbraco-forms-ready-on-july-20th-2021-at-7-am-utc/

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