CVE-2019-25337: OwnCloud Username Enumeration Vulnerability

CVE-2019-25337 Overview

CVE-2019-25337 is a username enumeration vulnerability affecting OwnCloud 8.1.8. This information disclosure flaw allows remote attackers to discover valid user accounts by manipulating the share.php endpoint. Attackers can send crafted GET requests to /index.php/core/ajax/share.php with a wildcard search parameter to retrieve comprehensive user information, potentially facilitating further targeted attacks against the affected system.

Critical Impact

Successful exploitation enables attackers to enumerate valid usernames on OwnCloud installations, which can be leveraged for credential stuffing, brute-force attacks, or targeted phishing campaigns against identified users.

Affected Products

• OwnCloud 8.1.8
• OwnCloud versions prior to security patches addressing this vulnerability

Discovery Timeline

• 2026-02-12 - CVE-2019-25337 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2019-25337

Vulnerability Analysis

This vulnerability is classified under CWE-203 (Observable Discrepancy), which describes conditions where an application reveals information through differences in system behavior. In the case of CVE-2019-25337, the OwnCloud share.php endpoint responds differently based on whether queried usernames exist in the system, allowing attackers to infer valid user accounts.

The vulnerability exists in OwnCloud's AJAX sharing functionality, specifically within the user search mechanism accessible via the /index.php/core/ajax/share.php endpoint. When an authenticated user (even with minimal privileges) sends a search request with wildcard characters, the application returns detailed user information without proper access controls or rate limiting.

Root Cause

The root cause of this vulnerability stems from insufficient access control on the user search functionality within OwnCloud's sharing module. The application fails to properly restrict which users can perform enumeration queries and does not implement adequate filtering on the search results returned to authenticated requesters. Additionally, the endpoint lacks protection against wildcard-based queries that can be used to harvest the complete user directory.

Attack Vector

This vulnerability is exploitable over the network by authenticated attackers with low privileges. The attack requires sending specially crafted HTTP GET requests to the vulnerable endpoint. By utilizing wildcard search parameters, an attacker can systematically extract usernames from the OwnCloud installation.

The attack flow involves:

1. Authenticating to the OwnCloud instance with any valid user account
2. Sending GET requests to /index.php/core/ajax/share.php with search parameters containing wildcards
3. Parsing the JSON response to extract valid usernames and associated user information
4. Using the harvested user list for follow-up attacks such as password spraying or phishing

For detailed exploitation information, refer to the Exploit-DB #47745 entry which documents the vulnerability mechanism.

Detection Methods for CVE-2019-25337

Indicators of Compromise

• Unusual volume of HTTP GET requests to /index.php/core/ajax/share.php from a single source
• Requests containing wildcard characters (e.g., %, *) in the search parameter
• Rapid sequential queries with incrementing or pattern-based search strings
• Failed login attempts for multiple usernames from the same IP address following enumeration activity

Detection Strategies

• Monitor web application logs for abnormal request patterns to the share.php endpoint
• Implement rate limiting detection rules for the user search functionality
• Configure Web Application Firewall (WAF) rules to flag requests with suspicious wildcard patterns
• Enable audit logging for user search operations within OwnCloud

Monitoring Recommendations

• Deploy SIEM rules to correlate high-volume share.php requests with subsequent authentication failures
• Establish baseline metrics for normal user search activity and alert on deviations
• Monitor for reconnaissance activity patterns that may indicate pre-attack information gathering
• Review authentication logs for credential stuffing attempts against enumerated usernames

How to Mitigate CVE-2019-25337

Immediate Actions Required

• Upgrade OwnCloud to a patched version that addresses the username enumeration vulnerability
• Implement network-level access controls to restrict access to administrative endpoints
• Enable and review audit logs for the sharing functionality
• Consider implementing additional authentication factors for sensitive operations

Patch Information

Organizations running OwnCloud 8.1.8 should upgrade to the latest supported version of OwnCloud that includes security fixes for this vulnerability. Consult the OwnCloud Official Website for current release information and upgrade guidance. The VulnCheck Advisory on OwnCloud provides additional context on the vulnerability disclosure.

Workarounds

• Restrict access to the share.php endpoint using web server configuration or reverse proxy rules
• Implement rate limiting on the user search functionality at the application or infrastructure level
• Deploy a Web Application Firewall (WAF) with rules to block wildcard-based enumeration attempts
• Consider disabling the user search feature if not required for business operations

# Apache configuration example to restrict access to share.php
<Location "/index.php/core/ajax/share.php">
    # Restrict to internal networks only
    Require ip 10.0.0.0/8
    Require ip 192.168.0.0/16
    Require ip 172.16.0.0/12
</Location>