argument %d exceeds maximum length (1024 characters)

Error message

argument %d exceeds maximum length (1024 characters)

What it means

ValidateStdioArgs limits each argument for MCP stdio transport to 1024 characters. This prevents oversized arguments from being used for buffer abuse, command-line injection payloads, or accidental resource exhaustion. The index of the offending argument (0-based) is included in the message.

Source

Thrown at internal/utils/security.go:568

	// Additional check: command should not contain path traversal
	if strings.Contains(command, "..") {
		return fmt.Errorf("command path contains invalid characters")
	}

	return nil
}

// ValidateStdioArgs validates the arguments for MCP stdio transport
// Returns an error if any argument contains dangerous patterns
func ValidateStdioArgs(args []string) error {
	if len(args) == 0 {
		return nil
	}

	for i, arg := range args {
		// Check length
		if len(arg) > 1024 {
			return fmt.Errorf("argument %d exceeds maximum length (1024 characters)", i)
		}

		// Check against dangerous patterns
		for _, pattern := range DangerousArgPatterns {
			if pattern.MatchString(arg) {
				return fmt.Errorf("argument %d contains potentially dangerous pattern: %s", i, SanitizeForLog(arg))
			}
		}

		// Check for null bytes
		if strings.Contains(arg, "\x00") {
			return fmt.Errorf("argument %d contains null bytes", i)
		}
	}

	return nil
}

View on GitHub (pinned to 988cbb0330)

Solutions

Shorten the argument: move long payloads into a file or env var and pass the path/var name instead
For inline code, write it to a temp script file and pass the file path as the argument
Split oversized arguments into multiple smaller arguments if the target program supports it
Use environment variables (validated separately, 4096-char limit) for long values

Example fix

// before
"args": ["-e", "<1500-char inline script>"]
// after
"args": ["/tmp/mcp-script.js"] // script content moved to file

Defensive patterns

Strategy: validation

Validate before calling

for i, a := range cfg.Args {
    if len(a) > 1024 {
        return fmt.Errorf("args[%d] too long (%d > 1024)", i, len(a))
    }
}

Try / catch

if err := ValidateStdioConfig(cfg); err != nil {
    var tooLongErr string = "exceeds maximum length"
    if strings.Contains(err.Error(), tooLongErr) {
        return fmt.Errorf("shorten stdio args or move payload to a file: %w", err)
    }
    return err
}

Prevention

Pass long payloads via files or env vars, not argv
Keep inline -e/-c scripts short; write them to temp files instead
Pre-check generated args for length before persisting configs

When it happens

Trigger: ValidateStdioConfig called with an args array where at least one element is longer than 1024 bytes (len(arg) in Go counts bytes, so multibyte UTF-8 hits the limit sooner).

Common situations: Passing long inline scripts (node -e, python -c) as arguments; embedding large URLs, tokens, or base64 blobs in args; configs generated programmatically that concatenate many values into one arg.

Related errors

AI-assisted analysis of Tencent/WeKnora@988cbb0330 (2026-09-02). Data as JSON: /api/errors/cd0bbb2f0827c440. Report an issue: GitHub.