CVE-2026-103522 in Thelia
Summary
by MITRE • 10/12/2026
In Thelia v2.6.0, the store banner upload feature performs insufficient filetype validation that relies exclusively on client‑supplied MIME types. An attacker with administrative access can upload a PHP file disguised as an image to bypass validation and achieve remote code execution on the underlying server.
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Analysis
by VulDB Data Team • 10/12/2026
The vulnerability in Thelia version 2.6.0 represents a critical failure in input validation mechanisms within the store banner upload functionality, specifically classified under CWE-434: Unrestricted Upload of File with Dangerous Type. This flaw stems from an insecure design pattern where the application relies exclusively on client-supplied MIME type headers to determine file validity rather than performing server-side content analysis or magic byte verification. By trusting the Content-Type header provided by the HTTP request, the system fails to verify that the actual binary data within the uploaded file matches the claimed media format. This architectural weakness allows an attacker who has obtained administrative privileges for the Thelia application to bypass security controls and execute arbitrary code on the hosting server.
From a technical perspective, this vulnerability exploits the discrepancy between metadata provided by the client and the actual content of the file. When a user uploads a banner image, the web browser or upload tool typically sends a MIME type such as image/jpeg or image/png in the HTTP header. The Thelia application accepts this value at face value without inspecting the file's internal structure to confirm it is indeed an image. Consequently, an attacker can craft a PHP script and rename it with an image extension like .jpg while setting the Content-Type header to match that of a legitimate image. Because the server does not validate the file signature or execute sandboxed checks on the payload content before storage, the malicious PHP file is saved directly into the web-accessible directory structure alongside other assets.
The operational impact of this vulnerability is severe, leading directly to Remote Code Execution (RCE). Once the disguised PHP file is stored in a location accessible via HTTP requests, an attacker can simply navigate to the URL corresponding to that uploaded file. The web server interprets the .php extension and executes the embedded code with the privileges of the web service account. This grants the attacker full control over the underlying operating system environment running Thelia. Depending on the configuration of the web server and the host machine, this can lead to complete compromise of the e-commerce platform, theft of sensitive customer data including payment information, installation of backdoors for persistent access, or use of the compromised server as a pivot point for further attacks against internal network resources. This aligns with MITRE ATT&CK technique T1505.003: Web Shell, where attackers upload malicious scripts to maintain persistence and execute commands remotely.
Mitigation strategies must focus on implementing robust file validation techniques that do not trust client-side inputs. The most effective approach is to perform server-side magic number verification, which involves reading the first few bytes of the uploaded file to identify its true format regardless of the MIME type header. Additionally, developers should enforce strict allowlists for permitted file extensions and ensure that uploaded files are stored in directories where script execution is disabled via web server configuration directives such as Apache's mod_mime or Nginx location blocks. Renaming uploaded files with random strings upon storage further reduces predictability and complicates exploitation attempts even if validation fails. Regular security audits of upload handlers and adherence to OWASP guidelines for file uploads are essential to prevent similar vulnerabilities in future releases.