Path Traversal in Cockpit CMS Bucket API

Executive Summary

CVE-2026-57856 is a path traversal vulnerability in Cockpit CMS, specifically in the Bucket file storage API located at /system/buckets/api. The vulnerability arises from insufficient sanitization of the bucket name parameter in the api() method of modules/System/Controller/Buckets.php.

The sanitization process uses preg_replace to remove characters that are not alphanumeric, hyphens, underscores, or periods, but it does not block directory traversal sequences like '..' or '../'. This allows an attacker to craft a malicious bucket name containing '../' sequences.

When the sanitized bucket name is interpolated into a Flysystem path (e.g., uploads://buckets/{bucket}), the '..' sequences are resolved by Flysystem's WhitespacePathNormalizer. This normalization process consumes the preceding 'buckets/' component, effectively allowing the attacker to traverse to the root of the uploads storage directory.

An authenticated low-privileged user can exploit this vulnerability to list, upload, or delete files across all buckets, including those belonging to other users or roles. This bypasses intended access controls and exposes sensitive data or allows unauthorized modifications.

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Detection Guidance

To detect the path traversal vulnerability in Cockpit CMS (CVE-2026-57856), you can check for suspicious activity or test the affected endpoint manually. Since the vulnerability allows authenticated low-privileged users to manipulate bucket names with '../' sequences, you can look for signs of exploitation or test the API endpoint.

• Check server logs for requests to /system/buckets/api with bucket names containing '../' or '..' sequences. Example log entry: POST /system/buckets/api?bucket=../../test.
• Use a tool like curl to send a test request to the vulnerable endpoint. Example command: curl -X POST -H "Authorization: Bearer YOUR_TOKEN" "http://YOUR_COCKPIT_INSTANCE/system/buckets/api?bucket=../". If the response includes files outside the intended bucket, the system is vulnerable.
• Inspect the Flysystem storage root (uploads directory) for unexpected files or modifications, as the vulnerability allows file operations outside the intended bucket scope.
• Use a vulnerability scanner that supports CVE-2026-57856 detection, though no specific tools are mentioned in the provided context.

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Impact Analysis

If you are using Cockpit CMS with the affected Bucket file storage API, this vulnerability can have several impacts:

• Unauthorized access to sensitive files: An attacker with low-privilege access can list or download files from other users' buckets, potentially exposing confidential or personal data.
• Data manipulation or deletion: The attacker can upload malicious files or delete existing files, leading to data loss, corruption, or unauthorized modifications.
• Privilege escalation: By accessing or modifying files belonging to higher-privileged users, the attacker may gain additional control over the system.
• System compromise: If the attacker uploads executable or malicious files, they could potentially execute arbitrary code on the server, leading to a full system compromise.

The impact is particularly severe because the vulnerability can be exploited remotely by any authenticated user, regardless of their privilege level.

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Compliance Impact

This vulnerability can have significant implications for compliance with various standards and regulations, depending on the type of data stored or processed by Cockpit CMS:

• GDPR (General Data Protection Regulation): If the CMS stores personal data of EU citizens, unauthorized access or exposure of this data due to the vulnerability could violate GDPR's data protection principles. This may result in hefty fines (up to 4% of global annual revenue or €20 million, whichever is higher) and mandatory breach notifications.
• HIPAA (Health Insurance Portability and Accountability Act): For organizations handling protected health information (PHI), this vulnerability could lead to unauthorized access or disclosure of PHI, violating HIPAA's Privacy and Security Rules. Non-compliance can result in fines ranging from $100 to $50,000 per violation, with a maximum penalty of $1.5 million per year.
• PCI DSS (Payment Card Industry Data Security Standard): If the CMS processes or stores payment card data, this vulnerability could lead to unauthorized access to cardholder data, violating PCI DSS requirements. Non-compliance can result in fines, increased transaction fees, or even the loss of the ability to process credit card payments.
• Other regulations: Depending on the industry and jurisdiction, this vulnerability could also impact compliance with standards like SOX (Sarbanes-Oxley Act), FISMA (Federal Information Security Management Act), or industry-specific regulations. Non-compliance may lead to legal penalties, reputational damage, or loss of business certifications.

Organizations must assess the data stored in Cockpit CMS and determine their compliance obligations. If the vulnerability is exploited, they may need to report the incident to regulatory bodies, affected individuals, or customers, depending on the applicable laws.

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Mitigation Strategies

To mitigate CVE-2026-57856, follow these immediate steps to reduce the risk of exploitation.

• Apply the official patch or update Cockpit CMS to the latest version if available. The provided context does not specify a patched version, so monitor the vendor's advisories for updates.
• Restrict access to the /system/buckets/api endpoint to trusted users only. Use network-level controls (e.g., firewalls, WAF rules) to block requests with '../' or '..' in the bucket parameter.
• Implement input validation to reject bucket names containing '../' or '..' sequences. Modify the sanitization logic in modules/System/Controller/Buckets.php to explicitly block these sequences.
• Monitor the uploads directory and bucket storage for unauthorized file changes or deletions. Restore affected files from backups if tampering is detected.
• Review user permissions and ensure low-privileged accounts do not have unnecessary access to the Bucket API. Consider disabling the API for non-administrative roles if not required.

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