CVE-2026-64798: Authentication Bypass Vulnerability

CVE-2026-64798 Overview

CVE-2026-64798 documents a cryptographic weakness in the generation of persistent URL login keys. The affected component produces these keys using a non-cryptographic pseudo-random number generator with insufficient entropy. This weakness is classified under CWE-338: Use of Cryptographically Weak Pseudo-Random Number Generator.

Attackers who can predict or brute-force the output space of the generator can forge valid persistent login URLs. A forged URL allows an attacker to authenticate as another user without knowing that user's password. The vulnerability affects functionality provided in Regular Labs components, as noted in the Regular Labs Security Overview.

Critical Impact
Predictable login tokens enable authentication bypass and account takeover through URL forgery.

Affected Products

Regular Labs component containing persistent URL login functionality
Specific affected versions are not enumerated in the published advisory data
Consult the vendor advisory for the authoritative fixed-version list

Discovery Timeline

2026-07-22 - CVE-2026-64798 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-64798

Vulnerability Analysis

The vulnerability resides in the routine that generates persistent URL login keys. Persistent login keys act as long-lived authentication tokens embedded in URLs. When a user clicks such a URL, the application accepts the embedded key as proof of identity and establishes a session.

Secure authentication tokens require unpredictability equivalent to a cryptographic secret. The affected code uses a non-cryptographic random source, typically a linear congruential generator or seeded PRNG intended for statistical sampling rather than security. The output space is small enough, or the seed predictable enough, that an attacker can enumerate candidate keys.

Once an attacker recovers or guesses a valid key, they submit the corresponding URL and obtain an authenticated session for the targeted user. No credential theft, phishing, or interaction with the victim is required.

Root Cause

The root cause is the choice of a non-cryptographic pseudo-random number generator to produce security-sensitive tokens. Non-cryptographic PRNGs, including PHP's rand() and mt_rand(), are deterministic given a known or guessable seed. They also expose short output widths that reduce the effective key space below the threshold required to resist online guessing. This category of flaw is tracked as [CWE-338].

Attack Vector

An unauthenticated remote attacker generates candidate persistent login URLs by reproducing the PRNG state or by brute-forcing the reduced key space. The attacker submits the crafted URL to the target application. When a candidate matches an active persistent key, the server issues a session bound to the corresponding user account. Successful exploitation yields account takeover, with impact scaling to administrative accounts if any administrator has enabled persistent URL login.

No verified proof-of-concept code has been published in the advisory data. Refer to the Regular Labs Security Overview for vendor-supplied technical detail.

Detection Methods for CVE-2026-64798

Indicators of Compromise

Repeated HTTP requests to persistent login endpoints with varying key parameters from a single source address
Successful authentications immediately following bursts of failed login-key submissions
Session establishments for user accounts from geolocations or user agents inconsistent with historical baseline
Access log entries containing sequentially structured or high-entropy key parameters at high request rates

Detection Strategies

Rate-limit and alert on repeated requests to the persistent-login URL handler, especially those varying only the key parameter
Correlate authentication success events with preceding volumes of authentication attempts from the same client
Inspect web server logs for enumeration patterns against the login-key query parameter

Monitoring Recommendations

Enable verbose authentication logging for persistent login flows, capturing source IP, user agent, and target account
Alert when a single account authenticates via persistent URL from multiple IPs within a short interval
Track the ratio of persistent-URL authentication attempts to successes, flagging anomalies at the site level

How to Mitigate CVE-2026-64798

Immediate Actions Required

Disable persistent URL login functionality in the affected component until a patched release is deployed
Invalidate all existing persistent login keys and force users to re-authenticate
Apply the vendor update as soon as Regular Labs publishes fixed versions
Review authentication logs for retroactive signs of key enumeration or unexpected session creation

Patch Information

Regular Labs is the maintainer of the affected component. Consult the Regular Labs Security Overview for the fixed version and upgrade instructions. Fixed builds replace the non-cryptographic PRNG with a cryptographically secure source such as random_bytes() and increase token length to resist brute-force enumeration.

Workarounds

Disable the persistent URL login feature at the application configuration level
Restrict access to persistent-login endpoints by source IP using web server or WAF rules
Shorten the lifetime of persistent tokens to reduce the window for enumeration attacks
Require a second authentication factor before honoring persistent login URLs for sensitive accounts

bash

# Example: block or rate-limit persistent login endpoint at the reverse proxy
# nginx snippet - adjust path to the affected handler
limit_req_zone $binary_remote_addr zone=login_keys:10m rate=5r/m;

location /index.php {
    if ($arg_task = "user.remember") {
        limit_req zone=login_keys burst=5 nodelay;
    }
}