CVE-2021-29842: IBM WebSphere Information Disclosure Flaw

CVE-2021-29842 Overview

IBM WebSphere Application Server contains a username enumeration vulnerability that allows remote attackers to identify valid usernames through differences in server responses between valid and invalid login attempts. This information disclosure vulnerability affects multiple versions of IBM WebSphere Application Server including traditional deployments and Liberty editions.

Critical Impact

Remote attackers can enumerate valid usernames without authentication, potentially enabling targeted brute-force attacks or social engineering campaigns against legitimate user accounts.

Affected Products

• IBM WebSphere Application Server 7.0
• IBM WebSphere Application Server 8.0
• IBM WebSphere Application Server 8.5
• IBM WebSphere Application Server 9.0
• IBM WebSphere Application Server Liberty 17.0.0.3 through 21.0.0.9

Discovery Timeline

• 2021-09-16 - CVE CVE-2021-29842 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-29842

Vulnerability Analysis

This vulnerability is classified under CWE-307 (Improper Restriction of Excessive Authentication Attempts), which relates to authentication mechanisms that fail to properly limit login attempts or that reveal user account information through response variations.

The core issue stems from inconsistent response behavior in the authentication system. When an attacker submits login requests, the server returns observably different responses depending on whether the username exists in the system. This differential response pattern—whether through timing differences, error message variations, HTTP status codes, or response content—enables systematic enumeration of valid user accounts.

The attack can be performed remotely over the network without any prior authentication, making it accessible to unauthenticated attackers. While the vulnerability itself does not directly compromise credentials, it significantly reduces the attack surface by allowing adversaries to identify valid targets for subsequent password guessing or credential stuffing attacks.

Root Cause

The root cause is improper handling of authentication error responses in IBM WebSphere Application Server. The authentication mechanism fails to normalize its responses between valid and invalid username scenarios, creating an information disclosure channel. Secure authentication implementations should return identical responses regardless of whether the username exists, using generic error messages such as "Invalid username or password" with consistent timing.

Attack Vector

The attack leverages the network-accessible login interface of IBM WebSphere Application Server. An attacker can systematically submit authentication requests with candidate usernames and analyze the server's responses to determine account validity. This enumeration can be automated using scripting tools that monitor for response variations including:

• Different HTTP status codes for valid vs. invalid usernames
• Variations in error message content or formatting
• Measurable timing differences in response delivery
• Different redirect behavior or page content

By compiling a list of valid usernames, attackers can then focus credential attacks on confirmed accounts, increasing the efficiency and likelihood of successful compromise.

Detection Methods for CVE-2021-29842

Indicators of Compromise

• High volume of failed authentication attempts from single IP addresses
• Sequential or systematic username patterns in login requests suggesting automated enumeration
• Unusual access patterns to authentication endpoints outside normal business hours
• Multiple failed login attempts across many different usernames in rapid succession

Detection Strategies

• Deploy web application firewalls (WAF) with rate limiting rules for authentication endpoints
• Implement anomaly detection for login attempt patterns that indicate enumeration activity
• Monitor authentication logs for systematic username testing patterns
• Configure SIEM rules to alert on threshold-based failed login attempts from single sources

Monitoring Recommendations

• Enable detailed logging for all authentication attempts including source IP, username, and response time
• Establish baseline metrics for normal authentication failure rates to identify anomalous spikes
• Implement real-time alerting for enumeration-like patterns targeting the WebSphere login mechanism
• Review authentication logs regularly for reconnaissance activity patterns

How to Mitigate CVE-2021-29842

Immediate Actions Required

• Apply IBM security patches for affected WebSphere Application Server versions immediately
• Implement account lockout policies to limit the value of enumerated usernames
• Deploy rate limiting on authentication endpoints to slow enumeration attempts
• Review and audit existing user accounts for compromise indicators

Patch Information

IBM has released security updates to address this vulnerability. Detailed patch information and installation instructions are available through the IBM Support Page for Node #6489485. Additional technical details can be found at the IBM X-Force Vulnerability #205202.

Organizations should prioritize patching based on the exposure level of their WebSphere deployments, with internet-facing instances requiring immediate attention.

Workarounds

• Implement CAPTCHA or similar challenge-response mechanisms on login pages to impede automated enumeration
• Configure uniform error messages and response times for all authentication failures regardless of username validity
• Use network-level controls to restrict access to authentication endpoints from untrusted networks
• Consider deploying additional authentication layers such as multi-factor authentication to reduce the impact of potential username enumeration

# Example rate limiting configuration for Apache HTTP Server fronting WebSphere
# Add to httpd.conf or virtual host configuration
<Location "/login">
    # Limit requests to 10 per minute per IP
    SetEnvIf Request_URI "^/login" rate_limit
    <IfModule mod_ratelimit.c>
        SetOutputFilter RATE_LIMIT
        SetEnv rate-limit 10
    </IfModule>
</Location>