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Umbraco CVE-2021-37334

CRITICAL
2021-08-25 cve@mitre.org
9.8
CVSS 3.1 · NVD
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Vulnerability Assessment

Impact

CVSS score of 9.8 (CRITICAL). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required.

Exploit ScenarioDerived

This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the critical-severity affected system.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
Patch available 2.7% exploitation probability (EPSS)

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AnalysisAI

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. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable, no authentication required, low attack complexity.

RemediationAI

A vendor patch is available. Apply the latest security update as soon as possible. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affects your stack

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Technical ContextAI · show details

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 include: Umbraco Forms. Version information: version 4.0.0.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 9.8 CRITICAL
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

DescriptionNVD

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.

Threat Intelligence Overview

EPSS Score
2.7%
Top 16% exploitable
Data Quality
2 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 2.7%
Patch available Yes
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
None
System Exposure· derived
Open
Automatable· derived
Yes
Human Impact· derived
Medium

Priority Score

52
Low Medium High Critical
KEV: 0
EPSS: +3
CVSS: +49
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.

Affected Products (CPE)NVD

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cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
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cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
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cpe:2.3:a:umbraco:forms:*:*:*:*:*:*:*:*
CVE-2012-10054 CRITICAL POC
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Umbraco CMS versions prior to 4.7.1 are vulnerable to unauthenticated remote code execution via the codeEditorSave.asmx

CVE-2015-8813 HIGH POC
8.2 Mar 03

The Page_Load function in Umbraco.Web/umbraco.presentation/umbraco/dashboard/FeedProxy.aspx.cs in Umbraco before 7.4.0 a

CVE-2020-9471 HIGH POC
8.8 Mar 16

Umbraco Cloud 8.5.3 allows an authenticated file upload (and consequently Remote Code Execution) via the Install Package

CVE-2021-47776 MEDIUM POC
6.9 Jan 15

Umbraco CMS v8.14.1 contains a server-side request forgery vulnerability that allows attackers to manipulate baseUrl par

CVE-2024-10761 MEDIUM POC
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A vulnerability was found in Umbraco CMS up to 10.7.7/12.3.6/13.5.2/14.3.1/15.1.1. Rated medium severity (CVSS 6.9), thi

CVE-2024-55488 MEDIUM POC
6.5 Jan 22

A stored cross-site scripting (XSS) vulnerability in Umbraco CMS v14.3.1 allows attackers to execute arbitrary web scrip

CVE-2020-5811 MEDIUM POC
6.5 Dec 30

An authenticated path traversal vulnerability exists during package installation in Umbraco CMS <= 8.9.1 or current, whi

CVE-2020-9472 MEDIUM POC
6.5 Mar 16

Umbraco CMS 8.5.3 allows an authenticated file upload (and consequently Remote Code Execution) via the Install Package f

CVE-2012-1301 CRITICAL
9.8 Apr 13

The FeedProxy.aspx script in Umbraco 4.7.0 allows remote attackers to proxy requests on their behalf via the "url" param

CVE-2015-8815 MEDIUM POC
6.1 Mar 03

Multiple cross-site scripting (XSS) vulnerabilities in Umbraco before 7.4.0 allow remote attackers to inject arbitrary w

CVE-2025-67288 CRITICAL
10.0 Dec 22

Arbitrary code execution in Umbraco CMS 16.3.3 is claimed via upload of a crafted PDF file that abuses insufficient file

CVE-2021-33224 CRITICAL
9.8 Feb 24

File upload vulnerability in Umbraco Forms v.8.7.0 allows unauthenticated attackers to execute arbitrary code via a craf

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