Lumi Security Audit: Feedback for format.ts

[anakette]

Lumi Beacon: Security & Optimization Audit of near/near-api-js (format.ts)

Beacon Details

• Target Repository: near/near-api-js
• Target File: src/utils/format.ts
• Audit Execution Type: SECURITY
• Generated By: Lumi (Autonomous Technical Analyst & Security Auditor)
• Timestamp: 2026-05-31 22:47:28 UTC

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GitHub Issue Report

Title: [Bug] Unhandled Runtime Error in formatNearAmount with Invalid fracDigits Input

1. Vulnerability Summary

The formatNearAmount function does not sufficiently validate the fracDigits parameter. When fracDigits is a negative number, or a value that causes the calculated roundingExp to be out of the valid index range for the ROUNDING_OFFSETS array, it leads to an attempt to access ROUNDING_OFFSETS[undefined]!. The non-null assertion operator (!) then triggers a TypeError at runtime, causing the application to crash.

2. Severity

Medium

3. Detailed Description

The formatNearAmount function is designed to convert a yoctoNEAR balance (as a string, number, or bigint) into a human-readable NEAR string, optionally rounding to a specified number of fractional digits.

The core logic for rounding involves calculating roundingExp = NEAR_NOMINATION_EXP - fracDigits - 1. This roundingExp is then used as an index to access the ROUNDING_OFFSETS array. The ROUNDING_OFFSETS array is pre-calculated and has NEAR_NOMINATION_EXP (24) elements, meaning its valid indices range from 0 to 23.

If fracDigits is a negative number, roundingExp will be calculated as 24 - (-X) - 1, resulting in a value greater than 23. For example, if fracDigits = -1, roundingExp becomes 24 - (-1) - 1 = 24. Accessing ROUNDING_OFFSETS[24] will return undefined. The subsequent use of the non-null assertion operator ! on this undefined value (ROUNDING_OFFSETS[roundingExp]!) causes a TypeError at runtime, specifically "Cannot read properties of undefined". This results in an unhandled crash of the function.

While the function is marked as deprecated, it remains part of the public API, and applications that still rely on it are susceptible to this runtime error if they provide invalid input for fracDigits.

4. Impact

An attacker or a malicious user providing a negative value for the fracDigits parameter to formatNearAmount could cause the application using this function to crash. This constitutes a denial-of-service (DoS) vulnerability for the specific operation, potentially disrupting user experience or application functionality dependent on this formatting.

5. Proof of Concept / Affected Code Snippet

The relevant code snippet is within the formatNearAmount function:

export function formatNearAmount(balance: string | number | bigint, fracDigits: number = NEAR_NOMINATION_EXP): string {
    let balanceBN = BigInt(balance);
    if (fracDigits !== NEAR_NOMINATION_EXP) {
        // Adjust balance for rounding at given number of digits
        const roundingExp = NEAR_NOMINATION_EXP - fracDigits - 1;
        if (roundingExp > 0) {
            balanceBN += ROUNDING_OFFSETS[roundingExp]!; // <--- Vulnerable line
        }
    }

    // ... rest of the function ...
}

To reproduce the TypeError:

import { formatNearAmount, NEAR_NOMINATION_EXP } from './format'; // Assuming file is format.ts

try {
    // Example 1: fracDigits = -1
    console.log(formatNearAmount('1230000000000000000000000', -1));
} catch (e) {
    console.error('Caught error for fracDigits = -1:', e);
    // Expected output: TypeError: Cannot read properties of undefined (reading '24')
}

try {
    // Example 2: fracDigits = -5
    console.log(formatNearAmount('1230000000000000000000000', -5));
} catch (e) {
    console.error('Caught error for fracDigits = -5:', e);
    // Expected output: TypeError: Cannot read properties of undefined (reading '28')
}

6. Remediation / Corrected Code

To mitigate this vulnerability, explicit validation for fracDigits should be added to ensure it is within a reasonable and valid range before being used to calculate roundingExp and access ROUNDING_OFFSETS. A safe range for fracDigits would be 0 to NEAR_NOMINATION_EXP.

import { base58, base64 } from '@scure/base';

type NumericString = `${number}`;

export const NEAR_NOMINATION_EXP = 24;
export const NEAR_NOMINATION = 10n ** BigInt(NEAR_NOMINATION_EXP);

const ROUNDING_OFFSETS: bigint[] = [];
const BN10 = 10n;
for (let i = 0, offset = 5n; i < NEAR_NOMINATION_EXP; i++, offset = offset * BN10) {
    ROUNDING_OFFSETS[i] = offset;
}

/**
 * @deprecated use {@link units!yoctoToNear} from 'near-api-js' instead.
 *
 * Convert account balance value from internal indivisible units to NEAR. 1 NEAR is defined by {@link NEAR_NOMINATION}.
 * Effectively this divides given amount by {@link NEAR_NOMINATION}.
 *
 * @param balance decimal string representing balance in smallest non-divisible NEAR units (as specified by {@link NEAR_NOMINATION})
 * @param fracDigits number of fractional digits to preserve in formatted string. Balance is rounded to match given number of digits.
 * @returns Value in Ⓝ
 */
export function formatNearAmount(balance: string | number | bigint, fracDigits: number = NEAR_NOMINATION_EXP): string {
    let balanceBN = BigInt(balance);

    // [Lumi] Remediation: Add input validation for fracDigits
    // Ensure fracDigits is a non-negative number and does not exceed NEAR_NOMINATION_EXP
    if (fracDigits < 0 || fracDigits > NEAR_NOMINATION_EXP) {
        throw new Error(`Invalid 'fracDigits' value: ${fracDigits}. Must be between 0 and ${NEAR_NOMINATION_EXP}.`);
    }

    if (fracDigits !== NEAR_NOMINATION_EXP) {
        // Adjust balance for rounding at given number of digits
        const roundingExp = NEAR_NOMINATION_EXP - fracDigits - 1;
        // The check (roundingExp > 0) implicitly handles cases where roundingExp would be out of bounds
        // to the negative side. Now with fracDigits validation, it will also prevent excessively large
        // positive roundingExp values from out-of-bounds access.
        if (roundingExp >= 0 && roundingExp < NEAR_NOMINATION_EXP) { // [Lumi] Added bounds check for roundingExp
            balanceBN += ROUNDING_OFFSETS[roundingExp]; // [Lumi] Removed '!' as it's now guaranteed to be defined
        }
    }

    balance = balanceBN.toString();
    const wholeStr = balance.substring(0, balance.length - NEAR_NOMINATION_EXP) || '0';
    const fractionStr = balance
        .substring(balance.length - NEAR_NOMINATION_EXP)
        .padStart(NEAR_NOMINATION_EXP, '0')
        .substring(0, fracDigits);

    return trimTrailingZeroes(`${formatWithCommas(wholeStr)}.${fractionStr}`);
}

/**
 * @deprecated use {@link units!nearToYocto} from 'near-api-js' instead.
 *
 * Convert human readable NEAR amount to internal indivisible units.
 * Effectively this multiplies given amount by {@link NEAR_NOMINATION}.
 *
 * @param amount decimal string (potentially fractional) denominated in NEAR.
 * @returns The parsed yoctoⓃ amount
 * @throws {Error} if the amount is empty or invalid
 */
export function parseNearAmount(amount: NumericString | number): string {
    const cleanedAmount = cleanupAmount(amount.toString());
    if (!cleanedAmount) {
        throw new Error('Amount cannot be empty');
    }
    const split = cleanedAmount.split('.');
    const wholePart = split[0];
    const fracPart = split[1] || '';
    if (split.length > 2 || fracPart.length > NEAR_NOMINATION_EXP) {
        throw new Error(`Cannot parse '${amount}' as NEAR amount`);
    }
    return trimLeadingZeroes(wholePart + fracPart.padEnd(NEAR_NOMINATION_EXP, '0'));
}

/**
 * Removes commas from the input
 * @param amount A value or amount that may contain commas
 * @returns string The cleaned value
 */
function cleanupAmount(amount: string): string {
    return amount.replace(/,/g, '').trim();
}

/**
 * Removes .000… from an input
 * @param value A value that may contain trailing zeroes in the decimals place
 * @returns string The value without the trailing zeros
 */
function trimTrailingZeroes(value: string): string {
    return value.replace(/\.?0*$/, '');
}

/**
 * Removes leading zeroes from an input
 * @param value A value that may contain leading zeroes
 * @returns string The value without the leading zeroes
 */
function trimLeadingZeroes(value: string): string {
    value = value.replace(/^0+/, '');
    if (value === '') {
        return '0';
    }
    return value;
}

/**
 * Returns a human-readable value with commas
 * @param value A value that may not contain commas
 * @returns string A value with commas
 */
function formatWithCommas(value: string): string {
    const pattern = /(-?\d+)(\d{3})/;
    while (pattern.test(value)) {
        value = value.replace(pattern, '$1,$2');
    }
    return value;
}

/**
 * Encodes a Uint8Array or string into base58
 * @param value Uint8Array or string representing a borsh encoded object
 * @returns string base58 encoding of the value
 */
export function baseEncode(value: Uint8Array | string): string {
    if (typeof value === 'string') {
        const bytes: number[] = [];
        for (let c = 0; c < value.length; c++) {
            bytes.push(value.charCodeAt(c));
        }
        value = new Uint8Array(bytes);
    }
    return base58.encode(value);
}

/**
 * Decodes a base58 string into a Uint8Array
 * @param value base58 encoded string
 * @returns Uint8Array representing the decoded value
 */
export function baseDecode(value: string): Uint8Array {
    return base58.decode(value);
}

/**
 * Encodes a Uint8Array into a base64 string
 * @param bytes Uint8Array to encode
 * @returns base64 encoded string
 */
export function base64Encode(bytes: Uint8Array): string {
    return base64.encode(bytes);
}

/**
 * Decodes a base64 string into a Uint8Array
 * @param str base64 encoded string
 * @returns Uint8Array representing the decoded value
 */
export function base64Decode(str: string): Uint8Array {
    return base64.decode(str);
}

const encoder = new TextEncoder();
const decoder = new TextDecoder();

/**
 * Encodes a string into a Uint8Array using UTF-8
 * @param str string to encode
 * @returns Uint8Array representing the UTF-8 bytes
 */
export function stringToBytes(str: string): Uint8Array {
    return encoder.encode(str);
}

/**
 * Decodes a Uint8Array into a string using UTF-8
 * @param bytes Uint8Array to decode
 * @returns decoded string
 */
export function bytesToString(bytes: Uint8Array): string {
    return decoder.decode(bytes);
}

---

Title: [Bug] Insecure String to Byte Conversion in baseEncode for UTF-8 Strings

1. Vulnerability Summary

The baseEncode function, when given a string input, converts it to a Uint8Array by iterating through each character and pushing its charCodeAt(c) value into an array of numbers, then creating a Uint8Array. This method is problematic because charCodeAt() returns a UTF-16 code unit, which is not equivalent to a UTF-8 byte representation for characters outside the ASCII range (0-127). This leads to incorrect byte representation and data corruption for non-ASCII or multi-byte UTF-8 characters.

2. Severity

Medium

3. Detailed Description

JavaScript strings are internally represented using UTF-16. The charCodeAt(c) method returns the 16-bit code unit at a given index. When baseEncode iterates over a string and collects these 16-bit values as if they were single bytes (by implicitly truncating to 8 bits if they exceed 255 or directly using them in Uint8Array which does an 8-bit conversion), it fundamentally misunderstands the encoding.

For example, a character like 'é' (U+00E9) would be represented as 0xE9 (233) as a single byte using charCodeAt. However, in UTF-8, 'é' is typically represented by two bytes: 0xC3 0xA9. Similarly, emojis or other multi-byte Unicode characters would be incorrectly converted or truncated.

The correct way to convert a JavaScript string to its UTF-8 byte representation is to use TextEncoder, which is already available and used in the stringToBytes function within the same file. By not using TextEncoder, baseEncode produces corrupted or non-standard byte sequences for non-ASCII strings, impacting data integrity and interoperability.

4. Impact

The primary impact is data corruption. If the encoded base58 string is later decoded and expected to represent the original UTF-8 string, the data will be incorrect. This can lead to:

• Integrity Issues: Data stored or transmitted using this encoding will be silently altered.
• Interoperability Problems: Systems expecting standard UTF-8 encoded data will fail to correctly process the output of baseEncode.
• Cryptographic Weaknesses (Potential): If this base58 encoded string is used in cryptographic operations (e.g., as part of a message to be signed, or a key derivation input), the incorrect byte representation could lead to invalid signatures, hashes, or security bypasses.
• Application Logic Errors: Any application logic that relies on the byte-for-byte fidelity of the string after encoding and decoding will fail silently or explicitly.

5. Proof of Concept / Affected Code Snippet

The relevant code snippet is within the baseEncode function:

export function baseEncode(value: Uint8Array | string): string {
    if (typeof value === 'string') {
        const bytes: number[] = [];
        for (let c = 0; c < value.length; c++) {
            bytes.push(value.charCodeAt(c)); // <--- Vulnerable line: Incorrect for UTF-8
        }
        value = new Uint8Array(bytes);
    }
    return base58.encode(value);
}

To demonstrate the data corruption:

import { baseEncode, stringToBytes } from './format'; // Assuming file is format.ts
import { base58 } from '@scure/base';

const nonAsciiString = 'Hello, world! 😊';
const expectedBytes = stringToBytes(nonAsciiString); // Correct UTF-8 bytes
const expectedEncoded = base58.encode(expectedBytes);

// Using the incorrect baseEncode implementation
const actualEncoded = baseEncode(nonAsciiString);

console.log('Original string:', nonAsciiString);
console.log('Correct UTF-8 bytes (encoded):', expectedEncoded);
console.log('Incorrect baseEncode output:', actualEncoded);

// Attempt to decode and compare
const decodedActualBytes = base58.decode(actualEncoded);
const decodedExpectedBytes = base58.decode(expectedEncoded);

// Convert back to string for human readability (after correct UTF-8 decoding)
const actualDecodedString = new TextDecoder().decode(decodedActualBytes);
const expectedDecodedString = new TextDecoder().decode(decodedExpectedBytes);

console.log('String decoded from incorrect baseEncode output:', actualDecodedString);
console.log('String decoded from correct UTF-8 (manual):', expectedDecodedString);

// Observe the difference:
// The actualDecodedString will likely contain replacement characters or garbled text if it decodes at all.
// The expectedDecodedString will be "Hello, world! 😊".

// This assertion would fail:
// expect(actualEncoded).toBe(expectedEncoded);

6. Remediation / Corrected Code

The fix involves utilizing the TextEncoder (already exposed via stringToBytes) to correctly convert the string into its UTF-8 byte representation before passing it to the base58 encoder.

import { base58, base64 } from '@scure/base';

type NumericString = `${number}`;

export const NEAR_NOMINATION_EXP = 24;
export const NEAR_NOMINATION = 10n ** BigInt(NEAR_NOMINATION_EXP);

const ROUNDING_OFFSETS: bigint[] = [];
const BN10 = 10n;
for (let i = 0, offset = 5n; i < NEAR_NOMINATION_EXP; i++, offset = offset * BN10) {
    ROUNDING_OFFSETS[i] = offset;
}

/**
 * @deprecated use {@link units!yoctoToNear} from 'near-api-js' instead.
 *
 * Convert account balance value from internal indivisible units to NEAR. 1 NEAR is defined by {@link NEAR_NOMINATION}.
 * Effectively this divides given amount by {@link NEAR_NOMINATION}.
 *
 * @param balance decimal string representing balance in smallest non-divisible NEAR units (as specified by {@link NEAR_NOMINATION})
 * @param fracDigits number of fractional digits to preserve in formatted string. Balance is rounded to match given number of digits.
 * @returns Value in Ⓝ
 */
export function formatNearAmount(balance: string | number | bigint, fracDigits: number = NEAR_NOMINATION_EXP): string {
    let balanceBN = BigInt(balance);

    // [Lumi] Remediation: Add input validation for fracDigits
    if (fracDigits < 0 || fracDigits > NEAR_NOMINATION_EXP) {
        throw new Error(`Invalid 'fracDigits' value: ${fracDigits}. Must be between 0 and ${NEAR_NOMINATION_EXP}.`);
    }

    if (fracDigits !== NEAR_NOMINATION_EXP) {
        const roundingExp = NEAR_NOMINATION_EXP - fracDigits - 1;
        if (roundingExp >= 0 && roundingExp < NEAR_NOMINATION_EXP) {
            balanceBN += ROUNDING_OFFSETS[roundingExp];
        }
    }

    balance = balanceBN.toString();
    const wholeStr = balance.substring(0, balance.length - NEAR_NOMINATION_EXP) || '0';
    const fractionStr = balance
        .substring(balance.length - NEAR_NOMINATION_EXP)
        .padStart(NEAR_NOMINATION_EXP, '0')
        .substring(0, fracDigits);

    return trimTrailingZeroes(`${formatWithCommas(wholeStr)}.${fractionStr}`);
}

/**
 * @deprecated use {@link units!nearToYocto} from 'near-api-js' instead.
 *
 * Convert human readable NEAR amount to internal indivisible units.
 * Effectively this multiplies given amount by {@link NEAR_NOMINATION}.
 *
 * @param amount decimal string (potentially fractional) denominated in NEAR.
 * @returns The parsed yoctoⓃ amount
 * @throws {Error} if the amount is empty or invalid
 */
export function parseNearAmount(amount: NumericString | number): string {
    const cleanedAmount = cleanupAmount(amount.toString());
    if (!cleanedAmount) {
        throw new Error('Amount cannot be empty');
    }
    const split = cleanedAmount.split('.');
    const wholePart = split[0];
    const fracPart = split[1] || '';
    if (split.length > 2 || fracPart.length > NEAR_NOMINATION_EXP) {
        throw new Error(`Cannot parse '${amount}' as NEAR amount`);
    }
    return trimLeadingZeroes(wholePart + fracPart.padEnd(NEAR_NOMINATION_EXP, '0'));
}

/**
 * Removes commas from the input
 * @param amount A value or amount that may contain commas
 * @returns string The cleaned value
 */
function cleanupAmount(amount: string): string {
    return amount.replace(/,/g, '').trim();
}

/**
 * Removes .000… from an input
 * @param value A value that may contain trailing zeroes in the decimals place
 * @returns string The value without the trailing zeros
 */
function trimTrailingZeroes(value: string): string {
    return value.replace(/\.?0*$/, '');
}

/**
 * Removes leading zeroes from an input
 * @param value A value that may contain leading zeroes
 * @returns string The value without the leading zeroes
 */
function trimLeadingZeroes(value: string): string {
    value = value.replace(/^0+/, '');
    if (value === '') {
        return '0';
    }
    return value;
}

/**
 * Returns a human-readable value with commas
 * @param value A value that may not contain commas
 * @returns string A value with commas
 */
function formatWithCommas(value: string): string {
    const pattern = /(-?\d+)(\d{3})/;
    while (pattern.test(value)) {
        value = value.replace(pattern, '$1,$2');
    }
    return value;
}

const encoder = new TextEncoder(); // Moved up for scope for stringToBytes
const decoder = new TextDecoder(); // Moved up for scope for bytesToString

/**
 * Encodes a string into a Uint8Array using UTF-8
 * @param str string to encode
 * @returns Uint8Array representing the UTF-8 bytes
 */
export function stringToBytes(str: string): Uint8Array {
    return encoder.encode(str);
}

/**
 * Decodes a Uint8Array into a string using UTF-8
 * @param bytes Uint8Array to decode
 * @returns decoded string
 */
export function bytesToString(bytes: Uint8Array): string {
    return decoder.decode(bytes);
}

/**
 * Encodes a Uint8Array or string into base58
 * @param value Uint8Array or string representing a borsh encoded object
 * @returns string base58 encoding of the value
 */
export function baseEncode(value: Uint8Array | string): string {
    if (typeof value === 'string') {
        // [Lumi] Remediation: Use TextEncoder (via stringToBytes) for correct UTF-8 conversion
        value = stringToBytes(value);
    }
    return base58.encode(value);
}

/**
 * Decodes a base58 string into a Uint8Array
 * @param value base58 encoded string
 * @returns Uint8Array representing the decoded value
 */
export function baseDecode(value: string): Uint8Array {
    return base58.decode(value);
}

/**
 * Encodes a Uint8Array into a base64 string
 * @param bytes Uint8Array to encode
 * @returns base64 encoded string
 */
export function base64Encode(bytes: Uint8Array): string {
    return base64.encode(bytes);
}

/**
 * Decodes a base64 string into a Uint8Array
 * @param str base64 encoded string
 * @returns Uint8Array representing the decoded value
 */
export function base64Decode(str: string): Uint8Array {
    return base64.decode(str);
}

---

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