critical CVSS 9.8 Actively exploited Public exploit available

CVE-2026-33017·Python vulnerability

Langflow is a tool for building and deploying AI-powered agents and workflows. In versions prior to 1.9.0, the POST /api/v1/build_public_tmp/{flow_id}/flow endpoint allows building public flows without requiring authentication. When the optional data parameter is supplied, the endpoint uses attacker-controlled flow data (containing arbitrary Python code in node definitions) instead of the stored flow data from the database. This code is passed to exec() with zero sandboxing, resulting in unauthenticated remote code execution. This is distinct from CVE-2025-3248, which fixed /api/v1/validate/code by adding authentication. The build_public_tmp endpoint is designed to be unauthenticated (for public flows) but incorrectly accepts attacker-supplied flow data containing arbitrary executable code. This issue has been fixed in version 1.9.0.

Severity
critical
Software
Python
Fixed in
1.8.2
Published
2026-03-20

Affected versions

Until: 1.8.2

Fixed in: 1.8.2

How to fix this CVE

Upgrade Langflow to version 1.9.0 or later immediately. If upgrading is not possible, disable public flow sharing or restrict access to the /api/v1/build_public_tmp endpoint via reverse proxy rules. Audit for signs of compromise.

pip install --upgrade langflow>=1.9.0
# Or via Docker:
docker pull langflowai/langflow:latest
# Verify: langflow --version (should show >= 1.9.0)
# Restrict endpoint if not upgrading:
# In nginx: location ~ /api/v1/build_public_tmp { deny all; }

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /api/v1/build_public_tmp/{flow_id}/flow HTTP/1.1
Content-Type: application/json

The attacker sends a crafted flow definition that includes malicious Python code in component configurations. When the server builds the flow, it executes the embedded code without authentication. The flow_id can be enumerated or guessed if public flows exist.

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

SecRule REQUEST_URI "@rx /api/v1/build_public_tmp" "id:20263301,phase:1,deny,status:403,msg:'CVE-2026-33017 Langflow pre-auth RCE endpoint blocked',severity:CRITICAL"

# Or restrict to authenticated users only via reverse proxy

How to check if you are affected

  1. Check Langflow version: langflow --version or pip show langflow — vulnerable if < 1.9.0
  2. Search for exploitation attempts in access logs: grep 'build_public_tmp' /var/log/nginx/access.log
  3. Check for running Langflow instances: ps aux | grep langflow
  4. Look for suspicious Python processes spawned by Langflow: pstree -p $(pgrep -f langflow)
  5. Check for newly created files in Langflow working directory
  6. Audit public flows: check Langflow UI for flows marked as public

Indicators of compromise

  • POST requests to /api/v1/build_public_tmp from external IPs
  • Langflow process spawning unexpected child processes (reverse shells, crypto miners)
  • New files created in Langflow temp directories or /tmp
  • Outbound connections from Langflow process to unknown IPs
  • Python subprocess execution triggered by flow builds

FAQ

Is Langflow widely deployed?

Langflow is a popular open-source tool for building AI/LLM workflows and agents. It has grown significantly with the AI/LLM boom and is used by developers, startups, and enterprises for prototyping and deploying AI pipelines.

Can this be exploited without any authentication?

Yes, that is what makes it critical. The build_public_tmp endpoint is accessible without authentication when public flows exist. An attacker only needs network access to the Langflow instance.

What can an attacker do with this vulnerability?

Full remote code execution on the server running Langflow. This typically means: data exfiltration, lateral movement, cryptocurrency mining, ransomware deployment, or establishing persistent backdoor access.

Does disabling public flows mitigate this?

Yes, if no public flows exist, the endpoint has no valid flow_id to target. However, upgrading is still recommended as a defense-in-depth measure.

Is this related to prompt injection?

No. This is a traditional code execution vulnerability in the application layer, not a prompt injection or LLM-specific attack. The flow build process executes Python code from flow definitions, and the endpoint lacks authentication.

Related Python CVEs

CVE-2026-33054CVSS 10Mesop is a Python-based UI framework that allows users to build web applications. Versions 1.2.2 and below contain a Path Traversal vulnerability that allows any user supplying an untrusted state_token through the UI stream payload to arbitrarily target files on the disk under the standard file-based runtime backend. This can result in application denial of service (via crash loops when reading non-msgpack target files as configurations), or arbitrary file manipulation. This vulnerability heavily exposes systems hosted utilizing FileStateSessionBackend. Unauthorized malicious actors could interact with arbitrary payloads overwriting or explicitly removing underlying service resources natively outside the application bounds. This issue has been fixed in version 1.2.3.
CVE-2026-32871CVSS 10FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. The RequestDirector class is responsible for constructing HTTP requests to the backend service. A vulnerability exists in the _build_url() method. When an OpenAPI operation defines path parameters (e.g., /api/v1/users/{user_id}), the system directly substitutes parameter values into the URL template string without URL-encoding. Subsequently, urllib.parse.urljoin() resolves the final URL. Since urljoin() interprets ../ sequences as directory traversal, an attacker controlling a path parameter can perform path traversal attacks to escape the intended API prefix and access arbitrary backend endpoints. This results in authenticated SSRF, as requests are sent with the authorization headers configured in the MCP provider. This issue has been patched in version 3.2.0.
CVE-2026-28505CVSS 10Tautulli is a Python based monitoring and tracking tool for Plex Media Server. Prior to version 2.17.0, the str_eval() function in notification_handler.py implements a sandboxed eval() for notification text templates. The sandbox attempts to restrict callable names by inspecting code.co_names of the compiled code object. However, co_names only contains names from the outer code object. When a lambda expression is used, it creates a nested code object whose attribute accesses are stored in code.co_consts, NOT in code.co_names. The sandbox never inspects nested code objects. This issue has been patched in version 2.17.0.
CVE-2026-34938CVSS 10PraisonAI is a multi-agent teams system. Prior to version 1.5.90, execute_code() in praisonai-agents runs attacker-controlled Python inside a three-layer sandbox that can be fully bypassed by passing a str subclass with an overridden startswith() method to the _safe_getattr wrapper, achieving arbitrary OS command execution on the host. This issue has been patched in version 1.5.90.
CVE-2026-25632CVSS 10EPyT-Flow is a Python package designed for the easy generation of hydraulic and water quality scenario data of water distribution networks. Prior to 0.16.1, EPyT-Flow’s REST API parses attacker-controlled JSON request bodies using a custom deserializer (my_load_from_json) that supports a type field. When type is present, the deserializer dynamically imports an attacker-specified module/class and instantiates it with attacker-supplied arguments. This allows invoking dangerous classes such as subprocess.Popen, which can lead to OS command execution during JSON parsing. This also affects the loading of JSON files. This vulnerability is fixed in 0.16.1.

References

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