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CVE-2026-85520 – Unauthenticated RCE via Arbitrary File Write – Google Merchant Center Feed (gmfeed)

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Summary

CVE-2026-85520 is a critical unauthenticated arbitrary file write vulnerability in the Google Merchant Center Feed (gmfeed) module for PrestaShop, developed by MyPresta. The flaw resides in the module’s feed.php endpoint, which fails to enforce authentication or validate attacker-supplied parameters that control the name, path, extension, and content of files written to the server. By submitting a crafted request, an unauthenticated attacker can write a PHP file to a web-accessible location and have it executed, resulting in full remote code execution (RCE) on the underlying store.

Technical details

  • Root cause: External control of file name or path (CWE-73) — the feed.php endpoint accepts request parameters that directly determine the output file’s name, directory path, and extension without sanitization or access control checks.
  • Trigger conditions: The module must be configured to generate catalog feeds via URL with the "save to file" option enabled; no valid session, API key, or credentials are required to reach the vulnerable endpoint.
  • Attack vector: Network-based, unauthenticated, low complexity — a single crafted HTTP request to feed.php is sufficient to plant a file.
  • Impact: Because the attacker fully controls the file extension and content, a .php file containing attacker-supplied code can be written into the webroot and subsequently invoked, giving the attacker arbitrary PHP code execution in the context of the web server (full compromise of confidentiality, integrity, and availability of the store and any data it processes, e.g. customer and payment-related data).

Affected software

  • Google Merchant Center Feed (gmfeed) module for PrestaShop, versions 1.9.1 through 2.3.8 (per the CVE record)
  • The vendor advisory further recommends any release below 2.3.10 be considered unsafe and upgraded

Severity

  • CVSS v4.0 Base Score: 9.3 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:L/SI:L/SA:L
  • Key drivers: network attack vector, no privileges or user interaction required, and high impact to confidentiality, integrity, and availability.

Mitigation and recommended actions

  • Immediate: Upgrade the gmfeed module to version 2.4.1 (the vendor’s advisory states 2.3.10 is the minimum patched version, with 2.4.1 as the current recommended release). Do not simply overwrite files — fully uninstall the existing module (including deleting old module files via the "delete module files" option in Module Manager) before installing the new package to ensure no vulnerable code remains.
  • After upgrading: Regenerate and replace any feed "Generate"/cron URLs used for save-to-file feed generation, since previously issued URLs are invalidated by the fix, and update any external integrations (cron jobs, Google Merchant Center feed URLs) accordingly.
  • If immediate patching is not possible: Disable the "save to file" / URL-based feed generation feature of the module, restrict or block external access to feed.php at the web server or WAF layer, and monitor the store’s file system and webroot for unexpected newly created PHP files.
  • General hygiene: Review server logs for anomalous POST/GET requests to feed.php predating the patch, and scan the PrestaShop installation for unauthorized files that may already have been planted.

References

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