CVE-2026-33309: langflow: Path Traversal enables file access
GHSA-g2j9-7rj2-gm6c CRITICAL CISA: ATTENDCVE-2026-33309 is a critical RCE in Langflow (CVSS 9.9) that bypasses the previously-issued patch for CVE-2025-68478. Any authenticated user — including trial accounts — can write arbitrary files to the host via a crafted multipart upload, leading to full system compromise. Upgrade to Langflow 1.9.0 immediately; if patching is not possible today, restrict access to the file upload endpoint and audit all authenticated accounts.
What is the risk?
CRITICAL. CVSS 9.9 with network-reachable attack vector, low complexity, and only low privilege required — meaning any authenticated user is a potential attacker. The Changed scope indicator signals cross-boundary impact: a compromise of the Langflow process can pivot to the underlying host, adjacent containers, or connected AI infrastructure. The fact that this is a patch bypass (not a novel discovery) raises the threat level further: defenders who believed they were protected by the CVE-2025-68478 fix are still exposed. Langflow is widely deployed in enterprise AI pipelines, RAG systems, and agent orchestration environments, significantly broadening blast radius.
What systems are affected?
| Package | Ecosystem | Vulnerable Range | Patched |
|---|---|---|---|
| Langflow | pip | >= 1.2.0, < 1.9.0 | 1.9.0 |
Do you use Langflow? You're affected.
How severe is it?
What is the attack surface?
What should I do?
6 steps-
PATCH
Upgrade Langflow to version 1.9.0 immediately — this is the only complete fix.
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WORKAROUND (if patching is delayed): Block or rate-limit POST /api/v2/files/ at the WAF/reverse proxy layer; require additional authentication for file upload operations.
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AUDIT
Review all user accounts with access to the Langflow instance; revoke unnecessary low-privilege accounts.
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DETECT
Monitor for unexpected file creation events outside Langflow's designated storage directory (e.g., writes to /etc/, /home/, Python site-packages, or cron directories); alert on new processes spawned by the Langflow service user.
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ISOLATE
Run Langflow in a minimal container with read-only filesystem mounts where possible; restrict the service account to least-privilege OS permissions.
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VERIFY
Scan your Langflow deployment logs for POST /api/v2/files/ requests with filenames containing '../', '%2e', encoded slashes, or absolute paths.
What does CISA's SSVC say?
Source: CISA Vulnrichment (SSVC v2.0). Decision based on the CISA Coordinator decision tree.
How is it classified?
Which compliance frameworks are affected?
This CVE is relevant to:
Frequently Asked Questions
What is CVE-2026-33309?
CVE-2026-33309 is a critical RCE in Langflow (CVSS 9.9) that bypasses the previously-issued patch for CVE-2025-68478. Any authenticated user — including trial accounts — can write arbitrary files to the host via a crafted multipart upload, leading to full system compromise. Upgrade to Langflow 1.9.0 immediately; if patching is not possible today, restrict access to the file upload endpoint and audit all authenticated accounts.
Is CVE-2026-33309 actively exploited?
No confirmed active exploitation of CVE-2026-33309 has been reported, but organizations should still patch proactively.
How to fix CVE-2026-33309?
1. PATCH: Upgrade Langflow to version 1.9.0 immediately — this is the only complete fix. 2. WORKAROUND (if patching is delayed): Block or rate-limit POST /api/v2/files/ at the WAF/reverse proxy layer; require additional authentication for file upload operations. 3. AUDIT: Review all user accounts with access to the Langflow instance; revoke unnecessary low-privilege accounts. 4. DETECT: Monitor for unexpected file creation events outside Langflow's designated storage directory (e.g., writes to /etc/, /home/, Python site-packages, or cron directories); alert on new processes spawned by the Langflow service user. 5. ISOLATE: Run Langflow in a minimal container with read-only filesystem mounts where possible; restrict the service account to least-privilege OS permissions. 6. VERIFY: Scan your Langflow deployment logs for POST /api/v2/files/ requests with filenames containing '../', '%2e', encoded slashes, or absolute paths.
What systems are affected by CVE-2026-33309?
This vulnerability affects the following AI/ML architecture patterns: agent frameworks, RAG pipelines, LLM orchestration platforms, AI workflow automation, model serving.
What is the CVSS score for CVE-2026-33309?
CVE-2026-33309 has a CVSS v3.1 base score of 9.9 (CRITICAL). The EPSS exploitation probability is 1.42%.
What is the AI security impact?
Affected AI Architectures
MITRE ATLAS Techniques
AML.T0010.001 AI Software AML.T0012 Valid Accounts AML.T0049 Exploit Public-Facing Application AML.T0050 Command and Scripting Interpreter AML.T0072 Reverse Shell AML.T0081 Modify AI Agent Configuration AML.T0083 Credentials from AI Agent Configuration AML.T0105 Escape to Host Compliance Controls Affected
What are the technical details?
Original Advisory
Langflow is a tool for building and deploying AI-powered agents and workflows. Versions 1.2.0 through 1.8.1 have a bypass of the patch for CVE-2025-68478 (External Control of File Name), leading to the root architectural issue within `LocalStorageService` remaining unresolved. Because the underlying storage layer lacks boundary containment checks, the system relies entirely on the HTTP-layer `ValidatedFileName` dependency. This defense-in-depth failure leaves the `POST /api/v2/files/` endpoint vulnerable to Arbitrary File Write. The multipart upload filename bypasses the path-parameter guard, allowing authenticated attackers to write files anywhere on the host system, leading to Remote Code Execution (RCE). Version 1.9.0 contains an updated fix.
Exploitation Scenario
An attacker with a low-privilege Langflow account (e.g., a compromised trial user or an insider threat) crafts a multipart HTTP POST to /api/v2/files/ with a filename such as '../../usr/lib/python3/dist-packages/langflow/malicious.py' or a path targeting a cron directory. The HTTP-layer ValidatedFileName check is bypassed because the underlying LocalStorageService performs no boundary containment — the filename passes through the storage layer unchanged. The server writes attacker-controlled Python code to the target path. On next Langflow process restart or scheduled execution, the injected module is imported and the attacker's payload executes with Langflow's process privileges. From there, the attacker establishes a reverse shell, exfiltrates API keys and LLM credentials stored in Langflow's configuration, poisons agent tool definitions to affect downstream AI pipeline consumers, and potentially pivots to connected databases or cloud infrastructure.
Weaknesses (CWE)
CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Primary
CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Primary
CWE-284 Improper Access Control
Primary
CWE-284 Improper Access Control
Primary
CWE-73 External Control of File Name or Path
Primary
CWE-73 External Control of File Name or Path
Primary
CWE-94 Improper Control of Generation of Code ('Code Injection')
Primary
CWE-94 Improper Control of Generation of Code ('Code Injection')
Primary
CWE-22 — Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'): The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
- [Implementation] Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylis
- [Architecture and Design] For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Source: MITRE CWE corpus.
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H References
Timeline
Related Vulnerabilities
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