FlowiseAI/Flowise · critical · Error

Invalid file path: null byte detected in "${key}"

Error message

Invalid file path: null byte detected in "${key}"

What it means

Thrown by getSafeFilePath() after percent-decoding the key, when the decoded value contains a NUL byte (\0). Null-byte injection is a classic technique to truncate a path or filename at the OS/C level so that a check sees one value but the syscall uses another; getSafeFilePath decodes first (so encoded %00 is caught too) and rejects the request outright rather than attempting to clean it.

Source

Thrown at packages/components/src/validator.ts:457

 * @param {string} baseDir The trusted base directory (e.g. a freshly created temp dir)
 * @param {string} key The untrusted relative key or filename
 * @returns {string} A validated absolute path guaranteed to be within baseDir
 * @throws {Error} If key is missing/invalid or the resolved path escapes baseDir
 */
export const getSafeFilePath = (baseDir: string, key: string): string => {
    if (!key || typeof key !== 'string') {
        throw new Error('Invalid file path: key is required and must be a string')
    }

    let decodedKey = key
    try {
        decodedKey = decodeURIComponent(key)
    } catch {
        // malformed percent-encoding — keep the raw key; resolve/relative handle it safely
    }

    if (decodedKey.includes('\0')) {
        throw new Error(`Invalid file path: null byte detected in "${key}"`)
    }

    const resolvedBase = path.resolve(baseDir)
    const resolvedPath = path.resolve(resolvedBase, decodedKey)

    if (process.env.PATH_TRAVERSAL_SAFETY === 'false') {
        return resolvedPath
    }

    const relative = path.relative(resolvedBase, resolvedPath)
    if (relative === '' || relative === '..' || relative.startsWith('..' + path.sep) || path.isAbsolute(relative)) {
        throw new Error(`Invalid file path: path traversal attempt detected in "${key}"`)
    }

    return resolvedPath
}

View on GitHub (pinned to abe4a8601a)

Solutions

1. Treat the request as malicious: reject with 400 and log the source IP / request id for investigation.
2. Ensure the key never carries binary/null data by validating the input charset (printable ASCII / UTF-8) at the request boundary.
3. Do not attempt to strip the null byte and continue — the presence itself indicates an attack; reject the whole request.

Example fix

// before
const abs = getSafeFilePath(baseDir, key) // throws on %00

// after
if (key.includes('\0') || /%00/i.test(key)) {
    logger.warn('Null-byte injection attempt blocked', { key, ip: req.ip })
    return res.status(400).json({ message: 'Invalid key' })
}
const abs = getSafeFilePath(baseDir, key)

// Reject null bytes in either raw or encoded form before resolving
if (typeof key !== 'string' || key.includes('\0') || /%00/i.test(key)) {
    logger.warn('Null-byte key blocked', { key, ip: req.ip })
    return res.status(400).json({ message: 'Invalid key' })
}

const hasNoNullByte = (v: unknown): v is string =>
    typeof v === 'string' && !v.includes('\0') && !/%00/i.test(v)

try {
    const abs = getSafeFilePath(baseDir, key)
} catch (e) {
    // null-byte presence is an attack — reject and log, never strip-and-retry
    return res.status(400).json({ message: 'Invalid file path' })
}

When it happens

Trigger: A key containing a literal \0; a key containing `%00` which decodes to \0 via decodeURIComponent; a key like `legit.txt%00.exe` intended to bypass extension checks. Reached when a client (or an attacker) supplies a URL-encoded null byte in a path/query param that flows into getSafeFilePath.

Common situations: Security scanning / fuzzing of file endpoints; legacy clients that include binary data in keys; a proxy that double-encodes the path. This is almost always indicative of a malicious or malformed request, not a normal user error.

Related errors

• Invalid or unsafe file name: ${name}
• Invalid file path: key is required and must be a string
• Invalid file path: path traversal attempt detected in "${key
• Failed to parse Supabase filter: ${error.message}
• Disallowed method: ${method}

AI-assisted analysis of FlowiseAI/Flowise@abe4a8601a (2026-08-12). Data as JSON: /api/errors/75996220c63ff3df. Report an issue: GitHub.