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GHSA-w794-rj3p-xv45 CVE-2026-105697 PYSEC-2026-4237 PYSEC-2026-4239 PYSEC-2026-4241

Langflow: OS command injection (RCE) via arbitrary command in MCP stdio server configuration

Critical PyPI
Severity
9.9 / 10
Critical · CVSS 3.1
Exploit chance (EPSS)
0.95%
Chance of exploitation in the next 30 days. Higher than 61.21% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-78 Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Fix
Available
3 packages have a fixed version

Description

Summary

Before Langflow 1.10.3, the MCP stdio transport launched whatever command / args a user put in an MCP server configuration, with no allowlist and (before 1.10.3) wrapped in bash -c "exec {command} ...". Any user able to reach the MCP server settings ("Settings → MCP Servers → Add MCP Server", POST/PATCH /api/v2/mcp/servers/{server_name}) or to build a flow with the MCP Tools component could add a "server" whose command is an arbitrary OS command (touch, rm -rf, a reverse shell, ...). The command runs on the Langflow host as the Langflow process user as soon as Langflow tries to connect to the server (listing servers, loading tools, running the flow) — even when the UI then reports that the stdio server failed to start.

With the default LANGFLOW_AUTO_LOGIN=true, GET /api/v1/auto_login hands out a token without credentials, so on an exposed instance running the default configuration this is reachable without an account. AUTO_LOGIN is documented as a development-only setting; with it disabled, any authenticated (non-admin) user can exploit it.

The issue was fixed in two steps and is fully fixed in Langflow 1.10.3 (and 1.11.0+):

  • 1.9.0 — #12290 added a command allowlist and argument/env validation to the REST model (MCPServerConfig), blocking the "Add MCP Server" vector reported here.
  • 1.10.3 — #14036 applied the same policy at the execution sink (lfx.base.mcp.util), including configs embedded in flows / tweaks and the final pre-spawn boundary, and removed the bash -c wrapper (the process is now exec'd directly, without a shell).

Affected versions

Package (PyPI) Vulnerable Patched
langflow >= 1.1.2, < 1.10.3 1.10.3
langflow-base >= 0.1.2, < 0.10.3 0.10.3
lfx < 1.10.3 1.10.3
Release State
1.1.2 – 1.4.x MCP Stdio component (added in #5148) runs StdioServerParameters(command=..., args=...) from the component's command field with no validation.
1.5.0 – 1.8.x "Add MCP Server" settings page and /api/v2/mcp/servers API added (#8388). Stored stdio configs are launched via bash -c "exec {command_str} ..." with no validation. The PoC below works as-is.
1.9.0 – 1.10.2 #12290: POST/PATCH /api/v2/mcp/servers reject commands outside the allowlist. The execution sink still has no validation and still uses bash -c, so configs that do not go through MCPServerConfig (for example an MCP Tools component value embedded in a flow or passed as a tweak) can still execute arbitrary commands.
1.10.3+ #14036: one shared policy (lfx.base.mcp.security.validate_mcp_stdio_config) is enforced at the API, at flow execution and right before the process is spawned; no shell is used. Fixed.

Details

Vulnerable sink (src/lfx/src/lfx/base/mcp/util.py, MCPStdioClient._connect_to_server, before 1.10.3):

server_params = StdioServerParameters(
    command="bash",
    args=["-c", f"exec {command_str} || echo 'Command failed with exit code $?' >&2"],
    env=env_data,
)

command_str is built from the user's command + args. The only "validation" before 1.9.0 was _validate_node_installation, which only checks that Node.js is installed when the command contains npx. The MCP SDK then starts the process with anyio.open_process, so the command runs before any MCP handshake — which is why it executes even if the UI shows "failed to start".

PoC (as reported, Langflow 1.5.0 – 1.8.x)

In "Add MCP Server" → STDIO, add:

Name      - Test
Command   - touch
Arguments - /tmp/pwn

Or through the API, using a token from auto_login (default configuration):

TOKEN=$(curl -s http://127.0.0.1:7860/api/v1/auto_login | python3 -c 'import sys,json;print(json.load(sys.stdin)["access_token"])')

curl -s -X POST 'http://127.0.0.1:7860/api/v2/mcp/servers/testing' \
  -H "Authorization: Bearer $TOKEN" \
  -H 'Content-Type: application/json' \
  --data-raw '{"command":"touch","args":["/tmp/pwned_langflow"]}'

/tmp/pwned_langflow gets created on the server. On 1.10.3+ the request is rejected with Command 'touch' is not allowed for security reasons. Allowed commands: bash, cmd, docker, node, npx, python, python3, uvx, and the same payload fails at the sink (MCPStdioClient.connect_to_server("touch /tmp/pwned_langflow") raises MCPStdioSecurityError, and no file is created). Wrappers such as bash -c "touch ...", sh -c ..., python3 -c ... and node -e ... are also rejected.

Fix

  • #12290 (1.9.0) — MCPServerConfig validators: command allowlist (node, python, python3, npx, uvx, docker, and cmd/sh/bash only to wrap one of those), shell-metacharacter and dangerous-keyword checks on arguments, env var blocklist (LD_PRELOAD, NODE_OPTIONS, PYTHONPATH, BASH_ENV, ...), and Docker isolation checks.
  • #14036 (1.10.3) — moves the policy into lfx.base.mcp.security.validate_mcp_stdio_config and enforces it at every entry point (API, embedded flow / tweak configs, the deprecated MCP Stdio component and just before spawn); it also launches the process without a shell:
command_parts = shlex.split(command_str)
command, args = command_parts[0], command_parts[1:]
validate_mcp_stdio_config(command, args, env)   # final pre-spawn enforcement
server_params = StdioServerParameters(command=command, args=final_args, env=env_data)

Later hardening (1.11.0, #13530) adds optional stricter modes for multi-tenant deployments.

Workarounds (if you cannot upgrade)

  • Set LANGFLOW_AUTO_LOGIN=false and do not expose Langflow directly to untrusted networks.
  • Only give Langflow accounts to trusted users.

Hardening recommendations for 1.10.3+

The allowlist still lets npx / uvx run any package by default, which is how MCP servers are normally distributed. On multi-tenant deployments, operators should also set:

  • LANGFLOW_MCP_SERVER_ALLOWED_PACKAGES — the exact packages npx / uvx may run.
  • LANGFLOW_MCP_SERVER_INTERPRETER_HARDENING=true and LANGFLOW_MCP_SERVER_DOCKER_HARDENING=true.
  • On 1.11.1+ (#14150), restricting custom code (LANGFLOW_ALLOW_CUSTOM_COMPONENTS=false, LANGFLOW_CUSTOM_COMPONENT_ADMIN_ONLY=true or LANGFLOW_BLOCK_CODE_INTERPRETER_COMPONENTS=true) also limits MCP stdio servers to superusers.

Impact

Remote code execution on the Langflow host as the Langflow process user (CWE-78). Any exposed instance on a vulnerable version is affected, whether the attacker has an account or uses the default AUTO_LOGIN. The reporter found several internet-facing Langflow servers that were vulnerable.

Affected versions

PyPI

PackageVulnerableFixed in
langflow
>= 1.1.2, < 1.10.3
1.10.3
langflow-base
>= 0.1.2, < 0.10.3
0.10.3
lfx
< 1.10.3
1.10.3

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

langflow PyPI → 1.10.3

pip
pip install --upgrade "langflow>=1.10.3"
poetry
poetry add "langflow>=1.10.3"
uv
uv add "langflow>=1.10.3"

langflow-base PyPI → 0.10.3

pip
pip install --upgrade "langflow-base>=0.10.3"
poetry
poetry add "langflow-base>=0.10.3"
uv
uv add "langflow-base>=0.10.3"

lfx PyPI → 1.10.3

pip
pip install --upgrade "lfx>=1.10.3"
poetry
poetry add "lfx>=1.10.3"
uv
uv add "lfx>=1.10.3"

Severity breakdown

CVSS 3.1 9.9

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

Weakness

CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

How to prevent it
  • Architecture and Design: If at all possible, use library calls rather than external processes to recreate the desired functionality.
  • Architecture and Design, Operation: Run the code in a "jail" or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software. OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations. This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise. Be careful to avoid CWE-243 and other weaknesses related to jails.
  • Architecture and Design: For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.
  • 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.
  • Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error.
  • Implementation: While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
  • Implementation: If the program to be executed allows arguments to be specified within an input file or from standard input, then consider using that mode to pass arguments instead of the command line.
  • Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. Some languages offer multiple functions that can be used to invoke commands. Where possible, identify any function that invokes a command shell using a single string, and replace it with a function that requires individual arguments. These functions typically perform appropriate quoting and filtering of arguments. For example, in C, the system() function accepts a string that contains the entire command to be executed, whereas execl(), execve(), and others require an array of strings, one for each argument. In Windows, CreateProcess() only accepts one command at a time. In Perl, if system() is provided with an array of arguments, then it will quote each of the arguments.
  • 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, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. When constructing OS command strings, use stringent allowlists that limit the character set based on the expected value of the parameter in the request. This will indirectly limit the scope of an attack, but this technique is less important than proper output encoding and escaping. Note that proper output encoding, escaping, and quoting is the most effective solution for preventing OS command injection, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent OS command injection, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, when invoking a mail program, you might need to allow the subject field to contain otherwise-dangerous inputs like ";" and ">" characters, which would ne
  • Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
  • Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
  • Operation: Run the code in an environment that performs automatic taint propagation and prevents any command execution that uses tainted variables, such as Perl's "-T" switch. This will force the program to perform validation steps that remove the taint, although you must be careful to correctly validate your inputs so that you do not accidentally mark dangerous inputs as untainted (see CWE-183 and CWE-184).
  • Implementation: Ensure that error messages only contain minimal details that are useful to the intended audience and no one else. The messages need to strike the balance between being too cryptic (which can confuse users) or being too detailed (which may reveal more than intended). The messages should not reveal the methods that were used to determine the error. Attackers can use detailed information to refine or optimize their original attack, thereby increasing their chances of success. If errors must be captured in some detail, record them in log messages, but consider what could occur if the log messages can be viewed by attackers. Highly sensitive information such as passwords should never be saved to log files. Avoid inconsistent messaging that might accidentally tip off an attacker about internal state, such as whether a user account exists or not. In the context of OS Command Injection, error information passed back to the user might reveal whether an OS command is being executed and possibly which command is being used.
  • Operation: Use runtime policy enforcement to create an allowlist of allowable commands, then prevent use of any command that does not appear in the allowlist. Technologies such as AppArmor are available to do this.
  • Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
  • Architecture and Design, Operation: Run your code using the lowest privileges that are required to accomplish the necessary tasks [REF-76]. If possible, create isolated accounts with limited privileges that are only used for a single task. That way, a successful attack will not immediately give the attacker access to the rest of the software or its environment. For example, database applications rarely need to run as the database administrator, especially in day-to-day operations.
  • Operation, Implementation: When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.

References

Advisories

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
CVE-2026-105740
Langflow is a tool for building and deploying AI-powered agents and workflows.
Critical Linked by the source
GHSA-qrpv-q767-xqq2
Langflow: IDOR Vulnerability in `/api/v1/responses` Endpoint Allows Authenticated Attackers to Access Another User's Flow
High Known exploited Also affects langflow
GHSA-vwmf-pq79-vjvx
Unauthenticated Remote Code Execution in Langflow via Public Flow Build Endpoint
Critical Known exploited Also affects langflow
GHSA-g22f-v6f7-2hrh
Langflow affected by Remote Code Execution via validate_code() exec()
High Known exploited Also affects langflow
GHSA-577h-p2hh-v4mv
Langflow CORS misconfiguration enables Account Takeover and RCE
Critical Known exploited Also affects langflow
GHSA-rvqx-wpfh-mfx7
Langflow Unauth RCE
Critical Known exploited Also affects langflow
GHSA-j8f7-x8jm-wmm4
Langflow: SSRF in URL-taking components (protection disabled by default / warn-only, not applied to RSS, SearXNG, Web Search, Home Assistant, Glean, Docling)
Medium Also affects langflow
GHSA-4f6c-2vvp-gw82
Langflow: IP Spoofing Bypass via `X-Forwarded-For` Allowing Remote Configuration Write
High Also affects langflow
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