CVE-2021-37334 [Critical]

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-11-21	0.89%	1.20%	+0.31%
2	2025-11-18	1.20%	0.89%	-0.31%
3	2025-03-30	—	1.20%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-11-21

0.89%

1.20%

+0.31%

2025-11-18

1.20%

0.89%

-0.31%

2025-03-30

—

1.20%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
9.8	3.1	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	3.9	5.9	[email protected]
9.3	2.0	HIGH	`AV:N/AC:M/Au:N/C:C/I:C/A:C` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:C) Complete confidentiality impact. Integrity impact (I:C) Complete integrity impact. Availability impact (A:C) Complete availability impact.	8.6	10.0	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

9.8

3.1

CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

3.9

5.9

[email protected]

9.3

2.0

HIGH

AV:N/AC:M/Au:N/C:C/I:C/A:C Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:C): Complete confidentiality impact.
Integrity impact (I:C): Complete integrity impact.
Availability impact (A:C): Complete availability impact.

8.6

10.0

[email protected]

Affected software / configurations for CVE-2021-37334

Vendor	Product	Version	Raw CPE
umbraco	forms	>= 4.0.0, < 4.4.9	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 6.0.0, < 6.0.10	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.0.0, < 7.0.7	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.1.0, < 7.1.4	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.2.0, < 7.2.1	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.3.0, < 7.3.2	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.4.0, < 7.4.3	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 7.5.0, < 7.5.4	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.0.0, < 8.0.2	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.1.0, < 8.1.6	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.2.0, < 8.2.3	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.3.0, < 8.3.4	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.4.0, < 8.4.4	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.5.0, < 8.5.7	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.6.0, < 8.6.2	cpe:2.3:a:umbraco:forms::::::::
umbraco	forms	>= 8.7.0, < 8.7.6	cpe:2.3:a:umbraco:forms::::::::

References for CVE-2021-37334

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

URL

CVE-2021-37334

Exploit prediction scoring system (EPSS) score for CVE-2021-37334

Common vulnerability scoring system (CVSS) metrics for CVE-2021-37334

Weakness enumeration for CVE-2021-37334

Affected software / configurations for CVE-2021-37334

References for CVE-2021-37334