Executive Summary

CVE-2026-54390 is a critical server-side template injection vulnerability in JTL Shop versions 5.2.0 through 5.7.1. It arises because unsanitized user input is passed to the Smarty template engine, allowing unauthenticated attackers to inject malicious template syntax.

Exploitation of this flaw can lead to attackers reading sensitive server-side information such as database credentials and encryption keys. In versions 5.4.0 through 5.7.1, attackers can also leverage registered Smarty modifiers like unserialize and file_get_contents to write a webshell to the web root and execute arbitrary commands as the web server user.

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Impact Analysis

This vulnerability can have severe impacts including unauthorized disclosure of sensitive data such as database credentials, encryption keys, and configuration details like SMTP or FTP settings.

For versions 5.4.0 to 5.7.1, attackers can achieve full unauthenticated remote code execution by writing a webshell to the server, allowing them to execute arbitrary commands as the web server user. This can lead to complete compromise of the affected server.

Affected users should upgrade immediately to patched versions or apply back-patches. After patching, it is recommended to rotate exposed secrets such as the Blowfish key and database passwords, and to scan for potential webshells or malware.

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Detection Guidance

To detect this vulnerability on your system, it is recommended to scan for potential webshells or malware that may have been uploaded by attackers exploiting the server-side template injection. Running specialized scanning tools like eComscan can help identify such malicious files or indicators of compromise.

Additionally, monitoring for unusual web requests that include suspicious template syntax or payloads targeting the Smarty template engine may help detect exploitation attempts.

Specific commands are not provided in the available resources, but using webshell detection scripts, file integrity monitoring, and scanning for known malicious patterns in web root directories are advisable.

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Mitigation Strategies

The immediate mitigation step is to upgrade JTL Shop to the latest patched versions: 5.5.4, 5.6.2, or 5.7.2, where the vulnerability has been fixed and backported.

If upgrading is not immediately possible, applying the back-patch provided for versions 5.0.0 through 5.7.0 is recommended.

After patching, it is important to rotate any potentially exposed secrets such as the Blowfish encryption key and database passwords, as these may have been compromised.

Deploying real-time protection tools like Sansec Shield can help block exploitation attempts while remediation is underway.

Finally, scanning your system for webshells or malware using tools like eComscan is advised to detect and remove any malicious code that may have been uploaded.

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Compliance Impact

The vulnerability allows unauthenticated attackers to read sensitive server-side values such as database credentials and encryption keys, and in some versions, to execute arbitrary commands on the server. This exposure of sensitive data and potential unauthorized access could lead to non-compliance with data protection regulations like GDPR and HIPAA, which require the protection of personal and sensitive information.

Specifically, the compromise of database credentials and encryption keys may result in unauthorized access to personal data, increasing the risk of data breaches. Such breaches can violate GDPR's requirements for data confidentiality and integrity, as well as HIPAA's mandates for protecting health information.

Therefore, organizations using affected versions of JTL Shop should urgently apply patches and rotate exposed secrets to mitigate risks and maintain compliance with these standards.

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