HSEC-2026-0011
Vulnerability from osv_haskell – Published: 2026-11-03 22:32 – Updated: 2026-11-03 22:32 – Source websiteSuperlinear encoding of numbers with large coefficients
Encoding (pretty-printing) a Scientific number whose coefficient has many
digits took time quadratic in the number of digits: the decimal digits were
extracted by repeatedly dividing the whole coefficient by 10, once per digit.
The Show instance, Data.Text.Lazy.Builder.Scientific and
Data.ByteString.Builder.Scientific — which aeson uses to encode JSON
numbers — all share this code path. A number with one million digits took
about a minute to show, and about a tenth of a second after the fix.
This is a denial-of-service risk for applications that decode numbers from an
untrusted source and encode them again, e.g. JSON proxies, loggers or API
gateways built on aeson.
Resolution
scientific-0.3.9.0 reimplemented normalize and toDecimalDigits (the
digit-extraction primitive) to be practically linear in the coefficient size.
Note that scientific-0.3.9.0 introduced a regression of its own; see
HSEC-2026-0012. Upgrade
directly to scientific-0.3.10.0 or later, which fixes both issues.
Credits
Reported by Andrzej Rybczak (@arybczak); fixed by Oleg Grenrus (@phadej).
{
"affected": [
{
"database_specific": {
"human_link": "https://github.com/haskell/security-advisories/tree/main/advisories/published/2026/HSEC-2026-0011.md",
"osv": "https://raw.githubusercontent.com/haskell/security-advisories/refs/heads/generated/osv-export/2026/HSEC-2026-0011.json"
},
"package": {
"ecosystem": "Hackage",
"name": "scientific"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.3.9.0"
}
],
"type": "ECOSYSTEM"
}
],
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
],
"database_specific": {
"home": "https://github.com/haskell/security-advisories",
"osvs": "https://raw.githubusercontent.com/haskell/security-advisories/refs/heads/generated/osv-export",
"repository": "https://github.com/haskell/security-advisories"
},
"details": "# Superlinear encoding of numbers with large coefficients\n\nEncoding (pretty-printing) a `Scientific` number whose coefficient has many\ndigits took time quadratic in the number of digits: the decimal digits were\nextracted by repeatedly dividing the whole coefficient by 10, once per digit.\nThe `Show` instance, `Data.Text.Lazy.Builder.Scientific` and\n`Data.ByteString.Builder.Scientific` \u2014 which `aeson` uses to encode JSON\nnumbers \u2014 all share this code path. A number with one million digits took\nabout a minute to show, and about a tenth of a second after the fix.\n\nThis is a denial-of-service risk for applications that decode numbers from an\nuntrusted source and encode them again, e.g. JSON proxies, loggers or API\ngateways built on `aeson`.\n\n## Resolution\n\n`scientific-0.3.9.0` reimplemented `normalize` and `toDecimalDigits` (the\ndigit-extraction primitive) to be practically linear in the coefficient size.\n\nNote that `scientific-0.3.9.0` introduced a regression of its own; see\nHSEC-2026-0012. Upgrade\ndirectly to `scientific-0.3.10.0` or later, which fixes both issues.\n\n## Credits\n\nReported by Andrzej Rybczak (@arybczak); fixed by Oleg Grenrus (@phadej).\n",
"id": "HSEC-2026-0011",
"modified": "2026-11-03T22:32:58Z",
"published": "2026-11-03T22:32:58Z",
"references": [
{
"type": "REPORT",
"url": "https://github.com/basvandijk/scientific/pull/109"
},
{
"type": "FIX",
"url": "https://github.com/basvandijk/scientific/pull/116"
},
{
"type": "FIX",
"url": "https://github.com/basvandijk/scientific/pull/117"
},
{
"type": "DISCUSSION",
"url": "https://www.reddit.com/r/haskell/comments/1xbj59g/dont_use_scientific_for_calculations_it_can/"
}
],
"related": [
"HSEC-2026-0012"
],
"schema_version": "1.5.0",
"summary": "Superlinear encoding of numbers with large coefficients"
}
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