CVE-2023-49105: ownCloud Server Auth Bypass Vulnerability

CVE-2023-49105 Overview

An authentication bypass vulnerability was discovered in ownCloud Server that allows unauthenticated attackers to access, modify, or delete any file on the system. The vulnerability exists in the WebDAV API's handling of pre-signed URLs when no signing-key is configured for a user. An attacker only needs to know a victim's username to exploit this flaw, making it trivially exploitable in environments where usernames are predictable or enumerable.

Critical Impact

Complete compromise of file confidentiality, integrity, and availability without authentication. Attackers can read, modify, or delete any file belonging to users who have no signing-key configured.

Affected Products

• ownCloud Server versions 10.6.0 through 10.13.0
• ownCloud owncloud/core component

Discovery Timeline

• 2023-11-21 - CVE-2023-49105 published to NVD
• 2025-04-02 - Last updated in NVD database

Technical Details for CVE-2023-49105

Vulnerability Analysis

This vulnerability represents a critical authentication bypass (CWE-287) in ownCloud Server's WebDAV API implementation. The flaw stems from improper validation of pre-signed URLs when the file owner has no signing-key configured. Pre-signed URLs are typically used to grant temporary, authenticated access to resources without requiring the user to provide credentials directly. However, ownCloud's implementation fails to properly reject pre-signed URL requests when the target user lacks a signing-key configuration.

The vulnerability allows complete bypass of authentication controls, enabling unauthorized access to the entire file system of affected users. This impacts all three pillars of information security—confidentiality (file reading), integrity (file modification), and availability (file deletion)—without requiring any prior authentication or user interaction.

Root Cause

The root cause lies in ownCloud's pre-signed URL validation logic. When processing a pre-signed URL request, the system should verify that the URL's signature matches the expected cryptographic signature generated using the file owner's signing-key. However, if no signing-key exists for the user, the validation logic fails to properly reject the request. Instead of treating a missing signing-key as an error condition that should deny access, the system permits the operation to proceed, effectively bypassing all authentication requirements.

Attack Vector

The attack exploits the WebDAV API endpoint over the network. An attacker needs only to:

1. Identify or enumerate a valid username on the ownCloud instance
2. Craft a pre-signed URL targeting that user's files
3. Submit the request to the WebDAV API

Since no signing-key exists for the target user, the signature validation is bypassed, granting the attacker full access to read, write, or delete files. The attack requires no authentication, no user interaction, and can be performed remotely over the network. Organizations with publicly accessible ownCloud instances and predictable username patterns are at heightened risk.

Detection Methods for CVE-2023-49105

Indicators of Compromise

• Unusual WebDAV API requests targeting multiple user accounts in rapid succession
• Pre-signed URL requests for users who have never configured signing-keys
• Unexpected file access, modification, or deletion patterns in ownCloud audit logs
• Anomalous access to sensitive files from unfamiliar IP addresses or geographic locations

Detection Strategies

• Monitor WebDAV API logs for pre-signed URL requests, particularly those targeting users without signing-keys configured
• Implement alerting on bulk file operations or access to files across multiple user accounts from a single source
• Review ownCloud access logs for requests originating from suspicious or external IP addresses
• Deploy network intrusion detection rules to identify malformed or suspicious pre-signed URL patterns

Monitoring Recommendations

• Enable comprehensive audit logging in ownCloud to capture all file access events
• Configure SIEM correlation rules to detect authentication bypass attempts via pre-signed URLs
• Establish baseline metrics for normal WebDAV API usage to identify anomalous activity
• Monitor for reconnaissance activities such as username enumeration attempts

How to Mitigate CVE-2023-49105

Immediate Actions Required

• Upgrade ownCloud Server to version 10.13.1 or later immediately
• Audit all user accounts to identify those without signing-keys configured
• Review recent file access logs for signs of unauthorized access or data exfiltration
• Consider temporarily restricting external access to ownCloud instances until patches are applied

Patch Information

ownCloud has released version 10.13.1 which addresses this vulnerability. Organizations should prioritize upgrading all affected instances. The security advisory is available at the OwnCloud Security Advisory page. Additional security information can be found at OwnCloud Security Updates.

Workarounds

• Ensure all user accounts have signing-keys properly configured to prevent exploitation
• Implement network-level access controls to restrict WebDAV API access to trusted IP ranges
• Deploy a web application firewall (WAF) with rules to inspect and block suspicious pre-signed URL requests
• Disable pre-signed URL functionality if not required for business operations

# Verify ownCloud version and check for available updates
sudo -u www-data php /var/www/owncloud/occ status
sudo -u www-data php /var/www/owncloud/occ upgrade

# Review users without signing-keys (consult ownCloud documentation for specific commands)
# Restrict access to ownCloud at the web server level if immediate patching is not possible