CVE-2021-28931Public exploitNetwork attack vector

Authenticated code execution via crafted theme archive

Published Jul 7, 2021 · Updated Aug 3, 2024

Arbitrary file upload in Fork CMS 5.9.2 and earlier allows remote authenticated users to write files under /themes via a crafted ZIP. The Themes panel's upload action extracts user-supplied archive entries without rejecting .htaccess, allowing server configuration and malicious code to be placed together. A valid backend account with theme-upload access is required; successful exploitation executes code in the web application context and exposes configuration-held database credentials.

CVSS severity8.8
High
EPSS probability1.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Arbitrary file upload in Fork CMS 5.9.2 and earlier allows remote authenticated users to write files under /themes via a crafted ZIP. The Themes panel's upload action extracts user-supplied archive entries without rejecting .htaccess, allowing server configuration and malicious code to be placed together. A valid backend account with theme-upload access is required; successful exploitation executes code in the web application context and exposes configuration-held database credentials.

The record

CVE
CVE-2021-28931
Published
Jul 7, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-434, CAPEC-1, T1505.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 7, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.8GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-434Unrestricted Upload of File with Dangerous Type
CAPEC-1Accessing Functionality Not Properly Constrained by ACLs
T1505.003Web Shell

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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