toml-node: Uncontrolled resource consumption (CPU DoS) via unbounded-length integer literals in toml.parse()

Summary

toml.parse() converts integer literals (hex, octal, binary, and decimal) to BigInt without first bounding the length of the digit sequence. Since BigInt(string) construction from a very long numeric string runs in super-linear time, a single small, well-formed TOML document containing one long integer literal can pin a Node.js process's event loop at 100% CPU for several seconds — a denial of service for any application that parses attacker-supplied or third-party TOML. No authentication or complex crafting is required.

Details

In lib/parser.js, the grammar actions that build integer nodes call BigInt() directly on the matched digit text, with no upper bound on its length:

• lib/parser.js:326 — hex: BigInt('0x' + stripUnderscores(digits))
• lib/parser.js:327 — octal: BigInt('0o' + stripUnderscores(digits))
• lib/parser.js:328 — binary: BigInt('0b' + stripUnderscores(digits))
• lib/parser.js:329 — decimal: BigInt(stripUnderscores(text))

The parser does enforce a nesting-depth limit (MAX_DEPTH, default 500, lib/parser.js:4343) to guard against stack overflow from deeply nested arrays/inline tables (per GHSA-82x6-q7mm-w9cf). However, that guard only bounds *structural nesting* — it does not bound the length of a single scalar token.

The subsequent 64-bit range check in lib/compiler.js (reduceInteger, lines 143–150, comparing against INT64_MIN / INT64_MAX defined at lines 3–4) happens after the expensive BigInt() conversion has already completed. It therefore provides no protection against this cost — the CPU time is already spent by the time the value is rejected as out of range.

PoC

const toml = require('toml');

const N = 5_000_000; // ~5 MB request body
const doc = 'x = 0x' + 'f'.repeat(N);

const start = Date.now();
try {
  toml.parse(doc); // eventually throws "outside the 64-bit signed integer range" —
                    // but only after the costly conversion has run
} catch (e) {}

console.log('elapsed:', Date.now() - start, 'ms');

Measured results:

| Digits (hex) | Approx. payload size | Parse time | |---:|---:|---:| | 200,000 | ~200 KB | 141 ms | | 400,000 | ~400 KB | 276 ms | | 800,000 | ~800 KB | 685 ms | | 1,600,000 | ~1.6 MB | 1,761 ms | | 5,000,000 | ~5 MB | 6,061 ms |

Growth is clearly super-linear. The same behavior reproduces for plain decimal literals (3,000,000 '9' digits → ~6.3 s).

Impact

Any application that calls toml.parse() on untrusted or third-party input — config upload endpoints, CI/CD tools ingesting user-supplied .toml files, package managers, linters, editors/language servers — is exposed.

During the conversion, the event loop is fully blocked. In a typical single-threaded Node.js server this stalls all concurrent request handling, not just the request containing the malicious payload. A single ~5 MB request is sufficient to cause several seconds of full CPU denial of service.

Suggested fix: Reject digit sequences above a reasonable length *before* calling BigInt(), analogous to the existing maxDepth option. A 64-bit signed integer requires at most 20 decimal digits or 16 hex digits, so any digit sequence significantly longer than that is guaranteed to fail the existing range check anyway, and can be rejected with a cheap .length comparison instead of paying for the full BigInt conversion.