CVE-2021-47735Public exploitNetwork attack vector

Authenticated code execution via template-file overwrite

Published Dec 23, 2025 · Updated Mar 5, 2026

Code injection in CMSimple 5.4 allows remote authenticated users to execute arbitrary PHP through the template editor. The authenticated edit action saves the unfiltered text field as the active template file, causing embedded PHP to execute when the site is requested. A valid login and editor-issued CSRF token are required; successful exploitation runs code with the web server process privileges.

CVSS severity8.6
High
EPSS probability0.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Code injection in CMSimple 5.4 allows remote authenticated users to execute arbitrary PHP through the template editor. The authenticated edit action saves the unfiltered text field as the active template file, causing embedded PHP to execute when the site is requested. A valid login and editor-issued CSRF token are required; successful exploitation runs code with the web server process privileges.

The record

CVE
CVE-2021-47735
Published
Dec 23, 2025
Updated
Mar 5, 2026
Vendor
CMSimple
Product
CMSimple
Classifications
CWE-94, T1505.003
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Dec 23, 2025CVE publishedPublication date reported by the CVE source.
  2. Mar 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=5.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

CMSimple · CMSimpleversion=5.4

Published CVSS scores

8.8VulnCheckCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.6VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1505.003Server Software Component: Web 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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