CVE-2026-42867 is a medium-severity (CVSS 6.5) Path Traversal vulnerability in langflow. A fix is available for langflow — see the affected versions and patch details below.
Langflow: Path Traversal in Knowledge Bases API via Creation Endpoint
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42867.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-42867 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
langflowReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
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.
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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | langflow | all versions | 1.9.0pip install --upgrade 'langflow==1.9.0' |
Affected Products
langflowlangflowDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for langflow, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update langflow to 1.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42867 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.
Frequently Asked Questions
Is CVE-2026-42867 in your dependencies?
Find it across PyPI, including transitive dependencies.