CVE-2023-22504: Confluence Server Auth Bypass Vulnerability

CVE-2023-22504 Overview

CVE-2023-22504 is a Broken Access Control vulnerability in Atlassian Confluence Server that allows remote attackers with read permissions to a page to upload attachments, even without write permissions. This security flaw in the attachments feature enables unauthorized file uploads, potentially compromising the integrity of Confluence content and introducing malicious files into the collaboration platform.

Critical Impact

Attackers with limited read-only access can bypass authorization controls to upload arbitrary attachments to Confluence pages, potentially enabling malware distribution, phishing attacks, or storage abuse within the enterprise wiki environment.

Affected Products

• Atlassian Confluence Server (multiple versions)

Discovery Timeline

• 2023-05-25 - CVE-2023-22504 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-22504

Vulnerability Analysis

This vulnerability represents a classic Broken Access Control flaw (CWE-434) where the Confluence Server fails to properly validate user permissions when processing attachment upload requests. The authorization logic incorrectly allows users with read-only access to a page to successfully upload attachments, a function that should be restricted to users with write permissions.

The vulnerability exploits a network-accessible endpoint that handles file attachments. An authenticated attacker with minimal privileges (read access only) can leverage this flaw to upload files to pages they should not be able to modify. This bypass of the expected permission model undermines the principle of least privilege and could have significant implications for organizations relying on Confluence's access control mechanisms to protect sensitive content areas.

Root Cause

The root cause of this vulnerability lies in improper access control validation within the Confluence attachment upload functionality. The application correctly verifies that a user has read access to a page before allowing attachment uploads but fails to additionally verify that the user has write permissions. This incomplete authorization check creates a gap between the intended permission model and the actual enforcement, allowing users to perform actions beyond their authorized scope.

Attack Vector

The attack vector is network-based, requiring only low-privilege authenticated access to the Confluence Server. An attacker would need valid credentials with read access to at least one Confluence page. The attack does not require user interaction and can be executed remotely against any affected Confluence Server instance accessible over the network.

The exploitation process involves:

1. Authenticating to the Confluence Server with a user account that has read-only access to a target page
2. Sending a crafted attachment upload request to the page's attachment endpoint
3. The server accepts the upload despite the user lacking write permissions

This vulnerability could be chained with other attacks, such as uploading malicious files that could be executed by other users or leveraging the attachment storage for phishing campaigns targeting other Confluence users.

Detection Methods for CVE-2023-22504

Indicators of Compromise

• Unexpected attachment uploads on Confluence pages, particularly from users with read-only access
• Anomalous file upload activity patterns from low-privilege user accounts
• Presence of suspicious or unexpected file types in Confluence attachments
• Audit log entries showing attachment creation by users who should only have read permissions

Detection Strategies

• Enable and monitor Confluence audit logs for attachment upload events, correlating with user permission levels
• Implement file upload monitoring to detect unusual patterns such as uploads from accounts typically restricted to read-only access
• Deploy network monitoring to identify HTTP POST requests to Confluence attachment endpoints from unexpected sources
• Regularly audit attachment histories across Confluence spaces to identify unauthorized uploads

Monitoring Recommendations

• Configure alerting for attachment upload events in sensitive Confluence spaces
• Implement periodic permission audits to ensure attachment upload activity aligns with expected user access levels
• Monitor for bulk or rapid attachment uploads that may indicate automated exploitation attempts
• Review Confluence server logs for attachment-related API calls from users with restricted permissions

How to Mitigate CVE-2023-22504

Immediate Actions Required

• Review the Atlassian Jira Issue CONFSERVER-83218 for the latest patch information and affected version details
• Update Atlassian Confluence Server to the latest patched version as recommended by Atlassian
• Audit existing Confluence attachments for any unauthorized uploads that may have occurred prior to patching
• Review user permissions across Confluence spaces to ensure appropriate access controls are in place

Patch Information

Atlassian has addressed this vulnerability in updated versions of Confluence Server. Organizations should consult the official Atlassian Jira Issue CONFSERVER-83218 for specific version information and download links for the security patches. It is strongly recommended to apply the official patch as the primary remediation measure.

Workarounds

• Restrict network access to Confluence Server to trusted networks and users until patching is complete
• Implement additional proxy-level controls to validate attachment upload requests against user permissions
• Consider temporarily disabling or restricting attachment functionality for read-only users if business requirements allow
• Enable enhanced audit logging to detect potential exploitation attempts while awaiting patch deployment