CVE-2026-25222: PolarLearn Timing Attack Vulnerability

CVE-2026-25222 Overview

PolarLearn is a free and open-source learning program that contains a timing attack vulnerability in its authentication process. In version 0-PRERELEASE-15 and earlier, the sign-in endpoint exhibits measurable response time differences that allow unauthenticated attackers to enumerate valid user email addresses on the platform.

By analyzing the response latency of login requests, attackers can distinguish between valid and invalid email addresses. This information disclosure vulnerability occurs because the server only performs computationally expensive Argon2 password hashing operations when the user exists in the database. Requests targeting existing users take approximately 650ms to process, while requests for non-existent users return in approximately 160ms—a difference of nearly 4x that is easily detectable.

Critical Impact

This timing attack enables attackers to build lists of valid user accounts, facilitating targeted credential stuffing attacks, phishing campaigns, and social engineering against confirmed platform users.

Affected Products

• PolarLearn 0-PRERELEASE-15 and earlier versions

Discovery Timeline

• 2026-02-02 - CVE CVE-2026-25222 published to NVD
• 2026-02-03 - Last updated in NVD database

Technical Details for CVE-2026-25222

Vulnerability Analysis

This vulnerability is classified under CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor). The root cause lies in the authentication flow's conditional execution of computationally intensive operations based on user existence.

When a login request is received, the application first queries the database to check if the provided email address corresponds to an existing account. If the user exists, the application proceeds to hash the submitted password using Argon2—a memory-hard hashing algorithm specifically designed to be computationally expensive to prevent brute-force attacks. However, if the user does not exist, the application skips this hashing step entirely and immediately returns an error response.

This asymmetric processing creates a measurable timing side-channel that leaks information about user account existence. The ~490ms timing differential between existing and non-existing users is substantial enough to be reliably detected even across network connections with moderate latency variance.

Root Cause

The vulnerability stems from a missing constant-time comparison pattern in the authentication logic. The application fails to perform equivalent computational work regardless of whether the user exists in the database. Best practice dictates that authentication systems should perform dummy password hashing operations for non-existent users to normalize response times and eliminate timing-based enumeration vectors.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can automate requests to the login endpoint with various email addresses, measuring response times for each. Statistical analysis of the response latencies reveals which email addresses correspond to registered accounts.

The attack methodology involves sending authentication requests with target email addresses and arbitrary passwords, then recording the response time for each request. Multiple samples per email address can be collected to account for network jitter and server load variations. Emails with consistently higher response times (around 650ms) indicate registered accounts, while those with faster responses (around 160ms) indicate non-existent accounts.

Detection Methods for CVE-2026-25222

Indicators of Compromise

• High volume of failed authentication attempts from single IP addresses or IP ranges targeting multiple email addresses
• Sequential or pattern-based email address testing in login request logs
• Requests with identical or minimal-effort passwords across many different email addresses
• Authentication endpoint traffic patterns showing systematic enumeration behavior

Detection Strategies

• Implement rate limiting monitoring on authentication endpoints with alerting for threshold violations
• Deploy anomaly detection for login request patterns that indicate enumeration activity
• Monitor for requests originating from known VPN, proxy, or hosting provider IP ranges targeting the login endpoint
• Analyze authentication logs for patterns of single-attempt failures across many unique email addresses

Monitoring Recommendations

• Enable detailed request timing logging on authentication endpoints to identify reconnaissance activity
• Implement SIEM rules to correlate failed login patterns indicative of user enumeration
• Configure alerts for authentication traffic spikes that may indicate automated enumeration tools
• Review authentication logs periodically for email address patterns suggesting dictionary-based enumeration

How to Mitigate CVE-2026-25222

Immediate Actions Required

• Upgrade PolarLearn to a version that includes the security fix from commit 6c276855172c7310cce0df996cb47ffe0d886741
• Implement aggressive rate limiting on authentication endpoints as a defense-in-depth measure
• Consider implementing CAPTCHA or similar challenges for repeated authentication failures
• Deploy Web Application Firewall (WAF) rules to detect and block enumeration attempts

Patch Information

The vulnerability has been addressed in the PolarLearn repository. The fix is available in commit 6c27685. Organizations running affected versions should update to a release that incorporates this fix. Full details are available in the GitHub Security Advisory GHSA-wcr9-mvr9-4qh5.

Workarounds

• Implement application-level rate limiting to restrict authentication attempts per IP address or session
• Deploy a reverse proxy or WAF with authentication rate limiting capabilities
• Consider implementing account lockout policies that trigger on repeated failures for the same email address
• Add artificial delay to all authentication responses to normalize timing (temporary mitigation until patch is applied)

# Example nginx rate limiting configuration for login endpoint
limit_req_zone $binary_remote_addr zone=login_limit:10m rate=5r/m;

location /api/auth/login {
    limit_req zone=login_limit burst=10 nodelay;
    limit_req_status 429;
    proxy_pass http://backend;
}