FlowiseAI/Flowise · error · Error

Argument '${arg}' contains flag '${flag}' that is not allowe

Error message

Argument '${arg}' contains flag '${flag}' that is not allowed for command '${command}'.

What it means

Thrown by validateCommandFlags when an arg starts with '<lowerCaseFlag>=' — the =-value form of a dangerous flag (e.g. '--node-options=...', '--env-file=...', '--volume=...', '--require=./evil'). The message names both the offending arg and the matched flag so the operator can see which entry in dangerousFlagsByCommand matched.

Source

Thrown at packages/components/nodes/tools/MCP/core.ts:389

    const dangerousFlags = dangerousFlagsByCommand[command] || []

    // Collect single-char dangerous flags (e.g. '-c' -> 'c') for combined flag detection
    const dangerousShortChars = new Set(dangerousFlags.filter((f) => /^-[a-zA-Z]$/.test(f)).map((f) => f[1].toLowerCase()))

    for (const arg of args) {
        if (typeof arg !== 'string') continue

        const normalizedArg = arg.toLowerCase().trim()

        // Check for dangerous flags in various forms (exact, =value, space-separated value)
        for (const flag of dangerousFlags) {
            const lowerCaseFlag = flag.toLowerCase()
            if (normalizedArg === lowerCaseFlag) {
                throw new Error(`Argument '${arg}' is not allowed for command '${command}'.`)
            }
            if (normalizedArg.startsWith(lowerCaseFlag + '=')) {
                throw new Error(`Argument '${arg}' contains flag '${flag}' that is not allowed for command '${command}'.`)
            }
            if (flag.startsWith('-') && normalizedArg.startsWith(lowerCaseFlag + ' ')) {
                throw new Error(`Argument '${arg}' contains flag '${flag}' that is not allowed for command '${command}'.`)
            }
        }

        // Check for combined short flags (e.g. "-yc" = "-y" + "-c")
        // A combined flag starts with a single '-', is not a long flag '--', and has multiple characters after '-'
        if (/^-[a-zA-Z]{2,}/.test(normalizedArg)) {
            const flagChars = normalizedArg.slice(1) // strip leading '-'
            for (const ch of flagChars) {
                if (dangerousShortChars.has(ch)) {
                    throw new Error(`Argument '${arg}' contains dangerous flag '-${ch}' for command '${command}'.`)
                }
            }
        }
    }
}

View on GitHub (pinned to abe4a8601a)

Solutions

1. Drop the dangerous flag entirely (do not pass --env-file/--volume/--require).
2. Pass the data through allow-listed env vars instead of file-loading flags.
3. If a mount is genuinely needed, run the MCP server outside the validated command path.

Example fix

// before
{ command: 'docker', args: ['run', '--volume=/host:/c', 'img'] }

// after
{ command: 'docker', args: ['run', 'img'] } // no host mount

const flags = (dangerousFlagsByCommand[command] ?? []).map(f => f.toLowerCase())
if (args.some(a => typeof a === 'string' && flags.some(f => a.toLowerCase().trim().startsWith(f + '=')))) {
  throw new Error(`Arg uses =value form of a dangerous flag for ${command}`)
}

const argsHaveNoDangerousEqValueFlags = (command: string, args: string[]): boolean => {
  const flags = (dangerousFlagsByCommand[command] ?? []).map(f => f.toLowerCase())
  return !args.some(a => typeof a === 'string' && flags.some(f => a.toLowerCase().trim().startsWith(f + '=')))
}

try {
  validateCommandFlags(command, args)
} catch (e) {
  if (e.message.includes("contains flag '") && e.message.includes("that is not allowed")) {
    // drop the offending flag=value token
  }
  throw e
}

When it happens

Trigger: validateCommandFlags processes an arg like '--env-file=/etc/passwd' for node, or '--volume=/:/x' for docker, and lowerCaseFlag + '=' matches a dangerous flag prefix.

Common situations: Operator tries to pass configuration via flag=value syntax to avoid the exact-match guard; docker --mount/--volume/--env-file; node --require/--loader with =.

Related errors

• Argument '${arg}' is not allowed for command '${command}'.
• Argument '${arg}' contains dangerous flag '-${ch}' for comma
• Argument contains potentially dangerous characters: "${arg}"
• Environment variable '${key}' contains null byte
• Security validation failed: ${error.message}

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/58947c945a4005a4. Report an issue: GitHub.