Summary
Langflow: Path Traversal in Knowledge Bases API via Creation Endpoint
Full technical description
Langflow is vulnerable to Path Traversal in the Knowledge Bases API (POST /api/v1/knowledge_bases). This occurs 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.
Details
The vulnerability exists in the create_knowledge_base function within src/backend/base/langflow/api/v1/knowledge_bases.py.
This function constructs file paths directly from the user-supplied name field without sanitization. The value is concatenated with the user's base directory and passed directly to kb_path.mkdir(). Immediately following the directory creation, the application writes embedding_metadata.json and schema.json into this attacker-controlled path.
PoC (Proof of Concept)
For the Create endpoint, an attacker can supply traversal sequences or absolute paths in the name field:
../victim_user/evil_kb
or/tmp/pwned
This forces kb_path.mkdir() to create directories and write specific application files (embedding_metadata.json and schema.json) at any reachable path on the server.
Fixes
The issue was addressed in PR #12337. The fix introduces the _validate_kb_path_containment() helper function, which uses Path.is_relative_to() instead of startswith() to enforce strict path boundaries and prevent prefix-ambiguity bugs. This helper is applied before any filesystem operations. Regression tests were added to verify that traversal payloads return a 403 Forbidden.
Acknowledgements
Thanks to the security researchers who responsibly disclosed this vulnerability:
- @ddlxstudio
- @nekros1xx
Impact
Any Langflow instance exposing this endpoint to authenticated users is vulnerable. This exposes the server to:
- Cross-user data compromise: Creation of directories and files within another tenant's knowledge base space.
- Arbitrary filesystem manipulation: Directory creation at any path on the server where the application has write permissions (e.g.,
/app/data). - Data overwrite: Overwriting existing
embedding_metadata.jsonandschema.jsonfiles in attacker-targeted paths, potentially corrupting existing knowledge bases.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-42867 has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.9.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2026-42867? CVE-2026-42867 is a medium-severity path traversal vulnerability in langflow (pip), affecting versions <= 1.8.4. It is fixed in 1.9.0. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-42867? CVE-2026-42867 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of langflow are affected by CVE-2026-42867? langflow (pip) versions <= 1.8.4 is affected.
- Is there a fix for CVE-2026-42867? Yes. CVE-2026-42867 is fixed in 1.9.0. Upgrade to this version or later.
- Is CVE-2026-42867 exploitable, and should I be worried? Whether CVE-2026-42867 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42867 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42867? Upgrade
langflowto 1.9.0 or later.