CVE-2026-53953: GetSimple CMS Auth Bypass Vulnerability

CVE-2026-53953 Overview

CVE-2026-53953 is a critical vulnerability in GetSimple CMS CE (Community Edition) version 3.3.22. The password reset endpoint is reachable without authentication and generates temporary passwords using PHP rand() seeded with microtime(). The limited seed space allows attackers to enumerate possible reset values. Because the admin login endpoint lacks rate limiting and account lockout, candidate passwords can be brute-forced online. Successful exploitation results in administrator account takeover. The flaw is tracked as CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator. No official patch is available at the time of publication.

Critical Impact

Unauthenticated attackers can predict temporary passwords generated during password resets and take over administrator accounts in GetSimple CMS CE 3.3.22.

Affected Products

• GetSimple CMS CE 3.3.22
• Community Edition installations exposing the password reset endpoint
• Deployments without upstream rate limiting on /admin/index.php

Discovery Timeline

• 2026-10-01 - CVE-2026-53953 published to the National Vulnerability Database
• 2026-10-05 - Last updated in NVD database

Technical Details for CVE-2026-53953

Vulnerability Analysis

The weakness resides in the password reset workflow of GetSimple CMS CE 3.3.22. When a reset request targets an existing user, the application generates a new temporary password, hashes it, and immediately replaces the stored user password. The endpoint requires no authentication, which means any remote actor can trigger a reset for a known administrator username. The temporary password is produced by PHP rand() seeded with microtime(). Because microtime() resolution is bounded and the seed space is small, attackers can enumerate plausible seeds and reproduce the generated password candidates offline. The admin login endpoint does not enforce request throttling or account lockout. Candidate passwords can then be submitted repeatedly until authentication succeeds, resulting in full administrator access.

Root Cause

The root cause is the use of a cryptographically weak pseudo-random number generator for a security-sensitive value, combined with a predictable time-based seed. PHP rand() is not suitable for generating secrets, and microtime() provides insufficient entropy to prevent brute-force reconstruction. Secure alternatives such as random_bytes() or random_int() would eliminate the predictability.

Attack Vector

An unauthenticated remote attacker submits a password reset request for a target administrator account. The attacker records the approximate time of the request, enumerates microtime() seeds within a bounded window, and reproduces the set of candidate temporary passwords. The attacker then automates login attempts against the admin login endpoint until the correct value is accepted. Full administrative control of the CMS follows.

No verified public exploit code is available. See the GitHub Security Advisory GHSA-vvhx-56q2-gcjq for additional technical details.

Detection Methods for CVE-2026-53953

Indicators of Compromise

• Unexpected POST requests to the GetSimple CMS CE password reset endpoint from external IP addresses
• Repeated failed authentication attempts against /admin/index.php from a single source within a short window
• Administrator password hashes changing without corresponding administrator-initiated activity
• New administrator sessions originating from unfamiliar geographies or hosting providers

Detection Strategies

• Alert on bursts of authentication failures followed by a successful login for the same administrator account
• Correlate password reset requests with subsequent high-volume login attempts from the same or related IPs
• Monitor file system changes to GetSimple CMS user data stores (data/users/*.xml) outside of change windows

Monitoring Recommendations

• Enable verbose web server access logging for the admin interface and retain logs for forensic review
• Forward web and application logs to a centralized analytics platform for correlation with authentication telemetry
• Baseline normal administrator login frequency and alert on deviations

How to Mitigate CVE-2026-53953

Immediate Actions Required

• Restrict access to the GetSimple CMS CE admin interface and password reset endpoint using IP allowlisting or VPN
• Disable or firewall the password reset functionality until a vendor fix is available
• Rotate all administrator credentials and audit the user data store for unauthorized changes
• Place the admin login endpoint behind a web application firewall that enforces rate limiting and account lockout

Patch Information

At the time of publication there are no publicly available patches for GetSimple CMS CE 3.3.22. Monitor the GitHub Security Advisory GHSA-vvhx-56q2-gcjq for updates and release notes from the GetSimple CMS CE project.

Workarounds

• Block the password reset endpoint at the reverse proxy or WAF layer
• Enforce strict rate limiting and progressive delays on /admin/index.php to defeat online brute force
• Require multi-factor authentication through an upstream identity provider or reverse proxy
• Remove or rename default administrator usernames to raise the cost of targeted resets

# Example NGINX configuration to rate limit the admin login endpoint
limit_req_zone $binary_remote_addr zone=gscms_admin:10m rate=5r/m;

server {
    location /admin/index.php {
        limit_req zone=gscms_admin burst=5 nodelay;
        limit_req_status 429;
    }

    # Block the password reset endpoint until a patch is available
    location = /admin/forgot_password.php {
        deny all;
        return 403;
    }
}