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CVE-2026-53952 – Unauthenticated Admin Account Creation – GetSimple CMS ≤3.4.0a / GetSimpleCMS-CE ≤3

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Summary

CVE-2026-53952 is a critical improper authorization vulnerability in GetSimple CMS and its community fork GetSimpleCMS-CE that allows a completely unauthenticated attacker to create a new administrator account. The flaw resides in the installation setup script, which the application fails to remove after initial setup due to a logic error in its own deletion routine, leaving it reachable and exploitable indefinitely. The issue carries a CVSS v3.1 base score of 9.8 (Critical).

Technical details

  • Root cause: after installation, GetSimple CMS is supposed to self-delete admin/setup.php as a safeguard. The deletion logic contains a self-exclusion check that skips deletion whenever setup.php itself is the script being executed, so the file is never actually removed.
  • setup.php additionally performs no authentication or configuration-state check before processing POST requests, so it will still process account-creation submissions after the site has already been set up.
  • Attack vector: a remote, unauthenticated attacker sends a crafted POST request directly to /admin/setup.php on an internet-exposed instance.
  • Impact: the attacker can create a new administrator account, gaining full administrative access to the CMS. This can lead to complete loss of confidentiality, integrity, and availability of the site, including content tampering, malware/webshell deployment, and full site takeover.

Affected software

  • GetSimple CMS: versions 3.4.0a and earlier
  • GetSimpleCMS-CE: versions 3.3.22 and earlier

Severity

  • CVSS v3.1 Base Score: 9.8 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: as of publication, no patched version has been released by either the GetSimple CMS or GetSimpleCMS-CE projects. Monitor vendor/project channels for an official fix and apply it as soon as it becomes available.
  • If no patch is available:
    • Manually delete or rename admin/setup.php (and any equivalent setup script) from the web root after installation, and verify it is not restored during updates.
    • Block external access to /admin/setup.php at the web server or WAF/reverse proxy layer.
    • Restrict access to the /admin/ directory to trusted IP ranges or place it behind additional authentication (e.g., HTTP basic auth, VPN).
    • Audit existing administrator accounts for any unauthorized/unrecognized entries and rotate credentials if compromise is suspected.

References

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