GHSA-R4XH-JQRQ-34V2
Vulnerability from github – Published: 2026-10-05 23:41 – Updated: 2026-10-05 23:41Summary
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
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": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 1.8.0"
},
"package": {
"ecosystem": "npm",
"name": "smol-toml"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.9.0"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-407"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-05T23:41:14Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Summary\n\n`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(\u0027.\u0027, 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).\n\nThe 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.\n\n### Proof of concept\n\n```js\nimport { parse } from \u0027smol-toml\u0027\n\nlet doc = \u0027\u0027\nfor (let i = 0; i \u003c 256000; i++) doc += \u0027k\u0027 + i + \u0027 = 1\\n\u0027\n\nconsole.time(\u0027parse\u0027)\nparse(doc) // ~2.8 MB of valid TOML, default options\nconsole.timeEnd(\u0027parse\u0027)\n```\n\nDoubling the line count roughly quadruples the time:\n\n| lines | size | parse() |\n|---|---|---|\n| 32k | 0.3 MB | 0.3 s |\n| 64k | 0.7 MB | 1.0 s |\n| 128k | 1.4 MB | 3.5 s |\n| 256k | 2.8 MB | 14 s |\n\n### Impact\nAny 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.\n\n### Patches\nVersion 1.9.0 uses a different implementation for parsing keys which is strictly linear.\n\n### Workarounds\nLimit the maximum document size accepted when parsing arbitrary documents.",
"id": "GHSA-r4xh-jqrq-34v2",
"modified": "2026-10-05T23:41:14Z",
"published": "2026-10-05T23:41:14Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/squirrelchat/smol-toml/security/advisories/GHSA-r4xh-jqrq-34v2"
},
{
"type": "WEB",
"url": "https://github.com/squirrelchat/smol-toml/commit/99102aa57fc932f760ea9c15b4cf1c181f952d24"
},
{
"type": "PACKAGE",
"url": "https://github.com/squirrelchat/smol-toml"
},
{
"type": "WEB",
"url": "https://github.com/squirrelchat/smol-toml/releases/tag/v1.9.0"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
"type": "CVSS_V3"
}
],
"summary": "smol-toml: Quadratic-time parse() from parseKey rescanning to end of document on each key line"
}
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