---
id: GHSA-r4xh-jqrq-34v2
title: >-
  smol-toml: Quadratic-time parse() from parseKey rescanning to end of document
  on each key line
summary: >-
  smol-toml: Quadratic-time parse() from parseKey rescanning to end of document
  on each key line
severity: medium
cvss: 5.3
cwe:
  - CWE-407
vendor: smol-toml
product: smol-toml
ecosystem: npm
affected:
  - smol-toml <= 1.8.0
patched:
  - smol-toml 1.9.0
published: '2026-10-05'
updated: '2026-10-05'
sourceUpdated: '2026-10-05T23:41:15Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-r4xh-jqrq-34v2'
references:
  - url: >-
      https://github.com/squirrelchat/smol-toml/security/advisories/GHSA-r4xh-jqrq-34v2
  - url: >-
      https://github.com/squirrelchat/smol-toml/commit/99102aa57fc932f760ea9c15b4cf1c181f952d24
  - url: 'https://github.com/squirrelchat/smol-toml/releases/tag/v1.9.0'
  - url: 'https://github.com/advisories/GHSA-r4xh-jqrq-34v2'
tags:
  - ghsa
  - npm
ingestedAt: '2026-10-06T00:37:36.241Z'
---

## Overview

### Summary

`parse()` has a quadratic-time path in `parseKey`, reachable on default options with ordinary valid input. For every key line and table-header line, `parseKey` (dist/struct.js, lines 58 and 86) finds the dotted-key separator with `ctx.s.indexOf('.', ctx.p)`, where `ctx.s` is the whole document. When a key has no `.` ahead of it, that search runs all the way to the end of the input, and the result is then clamped back to the line terminator `endPtr` - so everything scanned past the current line is wasted. `parseKey` runs once per line, so a document of N dot-free keys costs O(n^2).

The most ordinary TOML shape triggers it: a flat list of `key = value` lines, or a repeated `[[a]]` table. No dotted keys, no special options, valid input throughout.

### Proof of concept

```js
import { parse } from 'smol-toml'

let doc = ''
for (let i = 0; i < 256000; i++) doc += 'k' + i + ' = 1\n'

console.time('parse')
parse(doc) // ~2.8 MB of valid TOML, default options
console.timeEnd('parse')
```

Doubling the line count roughly quadruples the time:

| lines | size | parse() |
|---|---|---|
| 32k | 0.3 MB | 0.3 s |
| 64k | 0.7 MB | 1.0 s |
| 128k | 1.4 MB | 3.5 s |
| 256k | 2.8 MB | 14 s |

### Impact
Any service that runs `parse()` on attacker-supplied TOML can be stalled. The work is synchronous, so it blocks the whole event loop, and the quadratic is unbounded: a ~7 MB body pins a core for about a minute, larger bodies for several.

### Patches
Version 1.9.0 uses a different implementation for parsing keys which is strictly linear.

### Workarounds
Limit the maximum document size accepted when parsing arbitrary documents.

## Affected packages

- `smol-toml <= 1.8.0`

## Remediation

Upgrade to a patched release:

- `smol-toml 1.9.0`