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CVE-2021-37334: Umbraco Forms version 4.0.0 up to and including 8.7.5 and below are vulnerable to a security flaw that coul...

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

Affected Umbraco Forms installations can turn a file upload into server code execution or arbitrary file deletion. The flaw is dangerous because extension checks happen after temporary storage, allowing a crafted configuration file to change protections around the upload area.

Executive priority

Treat this as urgent for any affected Umbraco Forms deployment because compromise could lead to server takeover or destructive file deletion. Prioritize internet-facing sites and forms accepting uploads.

Technical view

Umbraco Forms 4.0.0 through 8.7.5 and below stores uploaded files under APP_DATA/TEMP/FileUploads before validating extensions. A crafted web.config in that temporary directory can override access restrictions, enabling malicious script upload, remote code execution, system command execution, and arbitrary file deletion.

Likely exposure

Exposure is likely limited to Umbraco sites running the affected Forms versions, especially deployments using form file uploads. The source does not identify affected CPEs or hosting environments beyond the Umbraco Forms version range.

Exploitation context

The bundle does not cite CISA KEV listing or active exploitation. Public CVE text describes a practical attack path, but does not state whether authentication or specific form permissions are required.

Researcher notes

Evidence is strong for vulnerability mechanics and affected version range, but incomplete for CVSS, CWE, authentication requirements, exploit prevalence, and exact patched version identifiers. Avoid assuming active exploitation without additional sources.

Mitigation direction

  • Apply the Umbraco Forms security patch referenced in the July 20, 2021 advisory.
  • Inventory Umbraco Forms versions and prioritize anything at or below 8.7.5.
  • Temporarily disable or restrict form file uploads until patched.
  • Review vendor guidance for supported patched versions and upgrade paths.
  • Restrict write and execute permissions around temporary upload directories.

Validation and detection

  • Confirm the installed Umbraco Forms version on every Umbraco site.
  • Identify public or internal forms that allow file uploads.
  • Check whether APP_DATA/TEMP/FileUploads exists under the application directory.
  • Review upload directories for unexpected web.config or script files.
  • Inspect server logs around form uploads for unusual file activity.
Prepared
Confidence
medium
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
description · low confidence lookup

File access behavior lookup

The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-37334 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.