CVE-2024-44762: Webmin Usermin User Enumeration Vulnerability

CVE-2024-44762 Overview

CVE-2024-44762 is an information disclosure vulnerability in Webmin Usermin version 2.100. The application returns different error messages for invalid login attempts depending on whether the submitted username exists. Attackers can exploit this discrepancy to enumerate valid user accounts on the target system without any authentication. Usermin is a web-based interface used for webmail, password changes, and other user-level administration tasks, making enumerated accounts a useful foothold for follow-on attacks such as credential stuffing or password spraying.

Critical Impact
Unauthenticated remote attackers can enumerate valid Usermin user accounts by observing differences in login error responses, enabling targeted brute-force and credential-stuffing attacks.

Affected Products

Webmin Usermin 2.100
Deployments exposing the Usermin login interface to untrusted networks
Systems using Usermin as a webmail or self-service password portal

Discovery Timeline

2024-10-16 - CVE-2024-44762 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-44762

Vulnerability Analysis

CVE-2024-44762 is an information disclosure issue classified under [CWE-209]: Generation of Error Message Containing Sensitive Information. The Usermin login handler in version 2.100 does not normalize its response when authentication fails. When an attacker submits credentials for an account that does not exist, the server returns a response that differs from the one produced when the account exists but the password is incorrect.

An unauthenticated attacker on the network can send successive login requests using a wordlist of candidate usernames. By comparing the returned error messages, response bodies, or HTTP timing characteristics, the attacker builds a list of valid accounts. This intelligence feeds directly into password-spraying campaigns against the same login endpoint.

While this weakness does not by itself grant access, it removes an important defensive layer. Login pages should treat authentication failure as a single outcome to avoid leaking account existence. Additional analysis of the login flow is available in the Sens Cybersecurity CVE-2024-44762 analysis.

Root Cause

The root cause is inconsistent error handling in the Usermin authentication routine. The code branches on whether a username lookup succeeds before proceeding to password verification, and each branch produces a distinguishable failure message. Secure authentication design requires that both branches emit an identical response and consume comparable processing time to prevent oracle behavior.

Attack Vector

Exploitation requires only network access to the Usermin web interface, which typically listens on TCP port 20000. No credentials, user interaction, or elevated privileges are needed. The attacker automates HTTP POST requests to the login endpoint with candidate usernames and arbitrary passwords, then parses responses to classify each username as valid or invalid. No verified proof-of-concept code is published in the referenced sources; the enumeration technique follows standard username-oracle patterns against the login form described in the vendor and third-party analyses.

Detection Methods for CVE-2024-44762

Indicators of Compromise

High volume of failed login attempts to the Usermin interface from a single source or small IP range within a short time window
Sequential login attempts iterating through common usernames such as admin, root, postmaster, and service accounts
Login requests from user agents associated with automation tools such as curl, python-requests, or hydra
Requests targeting /session_login.cgi or the Usermin authentication endpoint with rapid, uniform request timing

Detection Strategies

Parse Usermin and reverse-proxy access logs for repeated POST requests to the login endpoint returning authentication failure status codes
Correlate failed authentication events by source IP and count distinct usernames attempted per source within a rolling window
Alert when the ratio of unique usernames to attempts from a single client exceeds a baseline threshold
Compare response body sizes for login failures; consistent alternation between two response sizes indicates enumeration probing

Monitoring Recommendations

Forward Usermin access and error logs to a centralized logging platform for retention and correlation
Enable alerts on brute-force patterns targeting administrative web interfaces on non-standard ports such as 20000
Track first-seen usernames appearing in successful logins after periods of heavy failed-login activity from the same network range

How to Mitigate CVE-2024-44762

Immediate Actions Required

Upgrade Webmin Usermin beyond version 2.100 to a release that normalizes authentication error responses
Restrict network access to the Usermin interface using firewall rules, VPN, or reverse-proxy allowlists so only trusted networks can reach the login page
Enforce account lockout or rate limiting on repeated failed login attempts from a single source
Audit existing accounts and disable dormant or default usernames that adversaries commonly probe

Patch Information

No vendor advisory URL is included in the CVE record. Administrators should consult the Webmin project releases for versions later than Usermin 2.100 and apply the current stable release. Confirm after upgrade that invalid-user and invalid-password responses are indistinguishable in body, status code, and response time.

Workarounds

Place Usermin behind a reverse proxy that returns a uniform authentication failure page and enforces rate limiting on the login route
Require multi-factor authentication on any account permitted to reach the Usermin interface
Deploy a web application firewall rule that blocks or throttles clients exceeding a failed-login threshold per minute
Rename or remove predictable service accounts to reduce the utility of any successfully enumerated username list

bash

# Example: restrict Usermin port 20000 to a management subnet using iptables
iptables -A INPUT -p tcp --dport 20000 -s 10.0.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 20000 -j DROP

# Example: nginx reverse-proxy rate limit for the Usermin login endpoint
# In http { } block:
#   limit_req_zone $binary_remote_addr zone=usermin_login:10m rate=5r/m;
# In server { } block for the login location:
#   limit_req zone=usermin_login burst=5 nodelay;