multica-ai/multica · error

command_name cannot contain NUL bytes

Error message

command_name cannot contain NUL bytes

What it means

validateRuntimeProfileCommandName rejects command_name values containing a NUL byte. Same rationale as the fixed_args NUL check: Go strings carry NUL fine, but exec argv cannot, so a NUL would truncate the executable path at spawn time. Failing at validation surfaces the corruption immediately.

Solutions

1. Strip NULs and control characters from the command string before sending
2. Validate input is printable UTF-8 at the client boundary
3. Treat NUL in this field as a bug in the producer — find and fix the source of the binary data

Example fix

// before
commandName: buf.toString("utf8")
// after
commandName: buf.toString("utf8").replace(/[\x00\r\n]/g, "").trim()

if (commandName.includes('\x00')) {
  throw new Error('Corrupt input: NUL byte in executable name');
}

function isNulFreeCommand(s: string): boolean { return !s.includes('\x00'); }

When it happens

Trigger: POST/PUT a runtime profile whose command_name contains \u0000 — binary-corrupted input, fuzzed payloads, or a buffer decoded with the wrong encoding.

Common situations: Command read from a binary protocol or fixed-width record padded with NULs; encoding bugs (UTF-32 decoded as bytes); penetration-test payloads probing argv injection.

Related errors

• fixed_args entries cannot contain NUL bytes
• command_name is required
• command_name must be a single executable token; put…
• empty expected checksum for
• fixed_args entries must be non-empty

AI-assisted analysis of multica-ai/multica@2c0912b6ec (2026-08-15). Data as JSON: /api/errors/556686266ce48242. Report an issue: GitHub.

Appendix: source

Thrown at server/internal/handler/runtime_profile.go:111

			return nil, errors.New("fixed_args entries must be non-empty")
		}
		if strings.ContainsRune(a, '\x00') {
			return nil, errors.New("fixed_args entries cannot contain NUL bytes")
		}
		clean = append(clean, a)
	}
	return json.Marshal(clean)
}

func validateRuntimeProfileCommandName(commandName string) error {
	if commandName == "" {
		return errors.New("command_name is required")
	}
	if strings.ContainsAny(commandName, " \t\r\n") {
		return errors.New("command_name must be a single executable token; put arguments in fixed_args")
	}
	if strings.ContainsRune(commandName, '\x00') {
		return errors.New("command_name cannot contain NUL bytes")
	}
	return nil
}

type createRuntimeProfileRequest struct {
	DisplayName    string   `json:"display_name"`
	ProtocolFamily string   `json:"protocol_family"`
	CommandName    string   `json:"command_name"`
	Description    *string  `json:"description"`
	FixedArgs      []string `json:"fixed_args"`
	Enabled        *bool    `json:"enabled"`
}

// CreateRuntimeProfile creates a workspace runtime profile. Admin-gated by the
// router. protocol_family is validated against the agent backend whitelist.
func (h *Handler) CreateRuntimeProfile(w http.ResponseWriter, r *http.Request) {
	wsID := strings.TrimSpace(chi.URLParam(r, "id"))
	member, ok := h.requireWorkspaceMember(w, r, wsID, "workspace not found")

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