Compliance Impact

The vulnerability allows authenticated attackers to perform path traversal, enabling them to create directories and write files anywhere on the server's filesystem. This can lead to cross-user data compromise and arbitrary filesystem manipulation.

Such unauthorized access and potential data compromise could negatively impact compliance with data protection regulations like GDPR and HIPAA, which require strict controls on data confidentiality and integrity.

However, the provided information does not explicitly discuss compliance impacts or specific regulatory considerations.

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Executive Summary

CVE-2026-42867 is a Path Traversal vulnerability in the Langflow application's Knowledge Bases API (POST /api/v1/knowledge_bases). The issue arises because user-supplied knowledge base names are used directly to create file paths without proper sanitization or containment checks.

An authenticated attacker can exploit this flaw to create directories and write files anywhere on the server's filesystem by using path traversal sequences like ../ or absolute paths.

The vulnerability was fixed in Langflow version 1.9.0 by introducing a helper function that validates the constructed path to ensure it remains within the user's allowed directory space, preventing directory creation outside the designated area.

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Impact Analysis

This vulnerability allows an authenticated attacker to manipulate the filesystem on the server running Langflow by creating directories and writing files outside their authorized area.

• Cross-user data compromise by accessing or overwriting other users' data.
• Arbitrary filesystem manipulation, potentially leading to data corruption or unauthorized data injection.
• Overwriting critical files such as embedding_metadata.json and schema.json, which could disrupt application functionality or cause data loss.

Overall, this can lead to integrity and availability impacts on the system.

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Detection Guidance

This vulnerability can be detected by monitoring attempts to create knowledge bases with path traversal sequences in the POST /api/v1/knowledge_bases API requests. Look for directory names containing patterns like "../" or absolute paths such as "/tmp/" in the knowledge base name field.

Since the fix returns HTTP 403 Forbidden responses on path traversal attempts and logs security-relevant details, checking server logs for such 403 responses related to the knowledge bases API can help detect exploitation attempts.

Suggested commands to detect suspicious activity include:

• Use grep or similar tools to search server logs for 403 responses on the knowledge bases API endpoint, e.g., `grep 'POST /api/v1/knowledge_bases' /var/log/langflow/access.log | grep 403`.
• Monitor API request payloads for knowledge base names containing traversal sequences, e.g., `grep -E '\.\./|^/' /var/log/langflow/request_payloads.log`.
• Use file system monitoring tools to detect unexpected directory creations outside the expected knowledge base directories.

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Mitigation Strategies

The immediate mitigation step is to upgrade Langflow to version 1.9.0 or later, where the vulnerability is fixed by proper path validation and containment checks.

If upgrading immediately is not possible, restrict access to the Knowledge Bases API (POST /api/v1/knowledge_bases) to trusted users only, and monitor for suspicious path traversal attempts.

Additionally, review server logs for any signs of exploitation attempts and consider implementing network-level controls such as firewalls or API gateways to limit potentially malicious requests.

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