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How the mentioned CVE works:
The vulnerability exists within the handling of template closures in the `Contao\Template::once()` method. Backend users with template editing privileges can inject malicious closures into a template. When the vulnerable `once()` method is called, it executes the injected closure without properly validating its contents. This allows an attacker to call arbitrary PHP functions that do not require mandatory parameters through the closure, leading to remote code execution. The issue stems from insufficient sanitization of user-controlled input within the template rendering process, where the closure’s parameters are not checked before execution.
Platform: Contao
Version: 4.0.0-4.13.56
Vulnerability : Remote Code Execution
Severity: Moderate
date: 2025-11-25
Prediction: 2025-12-02
What Undercode Say:
curl -s https://contao.org/en/security-advisories/ | grep -i "template closure"
// Example vulnerable code structure
$template->once(function() use ($userInput) {
$userInput(); // Arbitrary function call
});
How Exploit:
1. Attacker gains backend access.
2. Edits a template file.
3. Injects malicious closure.
4. Closure executes arbitrary PHP code.
Protection from this CVE:
Update to patched versions.
Restrict backend template access.
Apply provided workaround patch.
Impact:
Arbitrary PHP execution.
System compromise.
Data manipulation.
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Sources:
Reported By: github.com
Extra Source Hub:
Undercode
