CVE-2026-93868: Cotonti CMS Auth Bypass Vulnerability

CVE-2026-93868 Overview

Cotonti through version 1.0.0 generates password recovery validation tokens using md5(microtime()) in users.passrecover.php. This weak pseudo-random number generator (PRNG) produces a predictable token space of roughly one million values per second. Unauthenticated attackers can read the server Date header, precompute candidate tokens within a narrow time window, and probe them against the passrecover endpoint. Successful token guessing allows an attacker to reset any account password, including administrator accounts, and take over the affected site. The weakness is classified under CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator.

Critical Impact
Unauthenticated attackers can reset arbitrary account passwords, including administrator accounts, resulting in full application takeover.

Affected Products

Cotonti CMS versions up to and including 1.0.0
modules/users/inc/users.passrecover.php password recovery component
Deployments relying on the default token generation routine

Discovery Timeline

2026-09-18 - CVE-2026-93868 published to NVD
2026-09-22 - Last updated in NVD database

Technical Details for CVE-2026-93868

Vulnerability Analysis

The password recovery flow in Cotonti derives its validation token by hashing the output of PHP's microtime() function with MD5. Because microtime() returns the current Unix timestamp with microsecond resolution, the effective entropy is bounded by the number of microseconds within the attack window. An attacker who can approximate the server clock reduces the search space to roughly one million tokens per second of uncertainty.

The HTTP Date response header exposes the server clock at second precision, allowing an attacker to anchor the search window without authentication. The attacker then triggers a password reset for the target account, enumerates candidate md5(microtime()) values for the observed second, and submits each token to the passrecover endpoint until one is accepted.

Root Cause

The root cause is the use of a non-cryptographic PRNG for a security-sensitive secret. MD5 is a fast, deterministic hash, and microtime() is not a source of unpredictable entropy. Secrets used for account recovery must be generated with a cryptographically secure random source such as random_bytes() and be long enough to resist brute-force enumeration.

Attack Vector

Exploitation is network-based and requires no prior authentication or user interaction beyond the attacker submitting a legitimate password reset request for the victim account. The attacker performs the following sequence:

Sends an HTTP request to the server and records the Date header value.
Requests password recovery for the target account through the standard reset workflow.
Computes md5(microtime()) for each microsecond within the estimated clock-skew window.
Submits candidate tokens against the passrecover validation endpoint until one succeeds.
Sets a new password for the compromised account and authenticates.

A sanitized code example is not published here. Refer to the VulnCheck Advisory on Cotonti and the vulnerable password recovery source for technical details.

Detection Methods for CVE-2026-93868

Indicators of Compromise

High volumes of requests to the passrecover endpoint from a single source address within a short time window.
Successful password changes for privileged accounts immediately following bursts of reset validation attempts.
New administrator sessions originating from IP addresses not previously associated with the account.

Detection Strategies

Deploy web server or WAF rules that count requests to the password recovery validation URL per source and per target user.
Alert on any single account receiving more than a small threshold of token validation attempts within a minute.
Correlate reset attempts with subsequent authentication events from the same source to identify successful takeovers.

Monitoring Recommendations

Log every access to users.passrecover.php with source IP, target user, token value, and outcome.
Forward web access logs to a centralized analytics platform for retention and anomaly detection.
Monitor administrator account changes (password updates, email changes, role modifications) as high-priority events.

How to Mitigate CVE-2026-93868

Immediate Actions Required

Upgrade Cotonti to a fixed release once available; track progress in Cotonti Issue #1890 and Pull Request #1898.
Force a password reset for all administrator and privileged accounts.
Rate-limit the password recovery endpoint at the reverse proxy or WAF layer.
Review recent password change events for unexplained modifications to privileged accounts.

Patch Information

A fix has been proposed upstream in Pull Request #1898 against the Cotonti repository. Administrators should apply the patched build once merged and released. Until then, replace the token generation logic in users.passrecover.php with a cryptographically secure routine using random_bytes(32) and bin2hex().

Workarounds

Modify modules/users/inc/users.passrecover.php locally to generate tokens with random_bytes() instead of md5(microtime()).
Suppress the HTTP Date header at the reverse proxy to increase attacker uncertainty about server clock state.
Restrict access to the password recovery endpoint by source IP or behind an authenticated portal where feasible.
Enforce strict rate limits and account lockouts on repeated failed token submissions per user.

bash

# Example nginx rate limit for the password recovery endpoint
limit_req_zone $binary_remote_addr zone=passrecover:10m rate=5r/m;

location ~* /users\.passrecover\.php$ {
    limit_req zone=passrecover burst=5 nodelay;
    proxy_hide_header Date;
    proxy_pass http://cotonti_backend;
}