gchq/CyberChef · error · OperationError

Error: Bit argument must be between 0 and 7

Error message

Error: Bit argument must be between 0 and 7

What it means

Thrown by the Extract LSB operation when the 'Bit' argument, after transformation (bit = 7 - args.pop()), falls outside the valid range [0, 7]. Each pixel channel value is 8 bits, so only bit positions 0–7 are valid for LSB extraction. The argument is popped from the end of the args array.

Source

Thrown at src/core/operations/ExtractLSB.mjs:86

     * @param {Object[]} args
     * @returns {byteArray}
     */
    async run(input, args) {
        if (!isImage(input))
            throw new OperationError("Please enter a valid image file.");

        const bit = 7 - args.pop(),
            pixelOrder = args.pop(),
            colours = args
                .filter((option) => option !== "")
                .map((option) => COLOUR_OPTIONS.indexOf(option)),
            parsedImage = await Jimp.read(input),
            width = parsedImage.bitmap.width,
            height = parsedImage.bitmap.height,
            rgba = parsedImage.bitmap.data;

        if (bit < 0 || bit > 7) {
            throw new OperationError(
                "Error: Bit argument must be between 0 and 7",
            );
        }

        let i,
            combinedBinary = "";

        if (pixelOrder === "Row") {
            for (i = 0; i < rgba.length; i += 4) {
                for (const colour of colours) {
                    combinedBinary += Utils.bin(rgba[i + colour])[bit];
                }
            }
        } else {
            let rowWidth;
            const pixelWidth = width * 4;
            for (let col = 0; col < width; col++) {
                for (let row = 0; row < height; row++) {

View on GitHub (pinned to 4290ea7539)

Solutions

1. Set the 'Bit' argument to an integer between 0 and 7 inclusive.
2. If using 0, note bit = 7 - 0 = 7 (most significant); if using 7, bit = 0 (least significant).
3. Validate the argument before running the operation.

Example fix

// before: args 'Bit' = 10 -> bit = 7 - 10 = -3 -> error

// after: args 'Bit' = 0 -> bit = 7 (valid range)

// Validate Bit argument before calling ExtractLSB
const bitArg = args[5];
if (typeof bitArg !== 'number' || bitArg < 0 || bitArg > 7) {
  throw new Error('Bit argument must be an integer between 0 and 7');
}

function isValidBitArg(bit) {
  return Number.isInteger(bit) && bit >= 0 && bit <= 7;
}

When it happens

Trigger: async run(input, args) where the computed bit value (7 - args[5], the 'Bit' number argument) is less than 0 or greater than 7. This means the raw 'Bit' argument was > 7 or < 0 before the 7-N transformation.

Common situations: User enters a Bit value of 8 or higher, or a negative number, in the operation's 'Bit' argument field. Also if a recipe programmatically supplies an out-of-range bit index.

Related errors

• Please enter a valid image file.
• Please enter a valid image file.
• Unsupported Mode: (${mode})
• Invalid file type.
• Invalid file type.

AI-assisted analysis of gchq/CyberChef@4290ea7539 (2026-08-13). Data as JSON: /api/errors/bf9f710b52c3a8c2. Report an issue: GitHub.