CVE-2021-35251: SolarWinds Web Help Desk Disclosure Flaw

CVE-2021-35251 Overview

CVE-2021-35251 is an information disclosure vulnerability affecting SolarWinds Web Help Desk. Sensitive information could be displayed when a detailed technical error message is posted, potentially disclosing environmental details about the Web Help Desk installation to unauthorized parties.

Critical Impact

Attackers can leverage verbose error messages to gather sensitive environmental information about the Web Help Desk installation, which could be used to facilitate further attacks against the target infrastructure.

Affected Products

• SolarWinds Web Help Desk (versions prior to 12.7.8)

Discovery Timeline

• 2022-03-10 - CVE-2021-35251 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-35251

Vulnerability Analysis

This vulnerability is classified under CWE-209 (Generation of Error Message Containing Sensitive Information). The core issue stems from improper handling of error conditions within the Web Help Desk application, where detailed technical error messages are exposed to users rather than being properly sanitized or logged internally.

When certain error conditions are triggered, the application generates verbose error messages that contain sensitive environmental details. This information could include server paths, configuration details, version information, or other technical metadata about the Web Help Desk installation. Such information is valuable for attackers performing reconnaissance activities and can significantly aid in the planning of subsequent attack phases.

The vulnerability is exploitable remotely over the network without requiring authentication or user interaction, making it accessible to any attacker who can reach the Web Help Desk installation.

Root Cause

The root cause of CVE-2021-35251 lies in improper error handling within the SolarWinds Web Help Desk application. When exceptions or errors occur during application processing, the error handling mechanism fails to properly sanitize or suppress technical details before presenting error messages to users. Instead of displaying generic error messages to end users while logging detailed information securely on the server side, the application exposes raw technical details that reveal information about the underlying environment.

Attack Vector

The attack vector for this vulnerability involves triggering error conditions in the Web Help Desk application through malformed requests or inputs that cause the application to generate detailed error messages. An attacker can access the application over the network without any prior authentication and deliberately craft requests designed to cause errors. When these errors occur, the verbose technical messages reveal environmental details that should remain confidential.

The disclosed information could include details such as:

• Internal file system paths
• Software version numbers and configurations
• Database connection information
• Server environment variables
• Stack traces revealing internal code structure

This reconnaissance data can be leveraged to identify additional vulnerabilities, plan targeted attacks, or understand the security posture of the installation.

Detection Methods for CVE-2021-35251

Indicators of Compromise

• Unusual volume of HTTP requests generating error responses from the Web Help Desk application
• Access logs showing repeated requests with malformed parameters or headers designed to trigger errors
• Error log entries indicating information disclosure events or verbose exception handling
• Network traffic analysis revealing sensitive system information in HTTP responses

Detection Strategies

• Monitor web server access logs for patterns of requests that consistently trigger error responses
• Implement web application firewall (WAF) rules to detect and alert on information disclosure in HTTP responses
• Review application error logs for evidence of detailed technical information being exposed
• Conduct periodic security assessments to identify verbose error handling configurations

Monitoring Recommendations

• Enable comprehensive logging on the Web Help Desk application and underlying web server
• Configure alerting for unusual patterns of error responses that may indicate reconnaissance activity
• Implement network monitoring to detect sensitive information patterns in outbound HTTP responses
• Regularly audit error handling configurations to ensure compliance with secure coding practices

How to Mitigate CVE-2021-35251

Immediate Actions Required

• Upgrade SolarWinds Web Help Desk to version 12.7.8 or later immediately
• Review error handling configurations to suppress verbose technical details in user-facing error messages
• Implement a web application firewall to filter sensitive information from error responses
• Restrict network access to the Web Help Desk installation to authorized users and networks only

Patch Information

SolarWinds has released a security patch addressing this vulnerability in Web Help Desk version 12.7.8. Organizations should upgrade to this version or later to remediate CVE-2021-35251. Detailed release notes and patch information are available in the SolarWinds WHD 12.7.8 Release Notes. Additional security advisory information is available at the SolarWinds Security Advisory for CVE-2021-35251.

Workarounds

• Configure custom error pages to display generic error messages without technical details
• Implement application-level filtering to sanitize error responses before delivery to clients
• Deploy a reverse proxy or WAF to intercept and sanitize error responses containing sensitive information
• Limit network exposure of the Web Help Desk application through firewall rules and network segmentation

# Example: Configure custom error pages in web server (Apache)
# Add to httpd.conf or .htaccess to suppress detailed error messages
ErrorDocument 400 /error/generic_error.html
ErrorDocument 403 /error/generic_error.html
ErrorDocument 404 /error/generic_error.html
ErrorDocument 500 /error/generic_error.html