readFloat: memory exhaustion with large exponent

{
  "affected": [
    {
      "database_specific": {
        "human_link": "https://github.com/haskell/security-advisories/tree/main/advisories/published/2023/HSEC-2023-0007.md",
        "osv": "https://raw.githubusercontent.com/haskell/security-advisories/refs/heads/generated/osv-export/2023/HSEC-2023-0007.json"
      },
      "package": {
        "ecosystem": "Hackage",
        "name": "base"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.0.3.1"
            }
          ],
          "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": {
        "human_link": "https://github.com/haskell/security-advisories/tree/main/advisories/published/2023/HSEC-2023-0007.md",
        "osv": "https://raw.githubusercontent.com/haskell/security-advisories/refs/heads/generated/osv-export/2023/HSEC-2023-0007.json"
      },
      "package": {
        "ecosystem": "Hackage",
        "name": "toml-reader"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.1.0.0"
            },
            {
              "fixed": "0.2.0.0"
            }
          ],
          "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": "# `readFloat`: memory exhaustion with large exponent\n\n`Numeric.readFloat` takes time and memory linear in the size of the\nnumber _denoted_ by the input string.  In particular, processing a\nnumber expressed in scientific notation with a very large exponent\ncould cause a denial of service.  The slowdown is observable on a\nmodern machine running GHC 9.4.4:\n\n```\nghci\u003e import qualified Numeric\nghci\u003e Numeric.readFloat \"1e1000000\"    -- near instantaneous\n[(Infinity,\"\")]\nghci\u003e Numeric.readFloat \"1e10000000\"   -- perceptible pause\n[(Infinity,\"\")]\nghci\u003e Numeric.readFloat \"1e100000000\"  -- ~ 3 seconds\n[(Infinity,\"\")]\nghci\u003e Numeric.readFloat \"1e1000000000\" -- ~ 35 seconds\n[(Infinity,\"\")]\n```\n\n## In *base*\n\n`Numeric.readFloat` is defined for all `RealFrac a =\u003e a`:\n\n```haskell\nreadFloat :: RealFrac a =\u003e ReadS a\n```\n\nThe `RealFrac` type class does not express any bounds on the size of\nvalues representable in the types for which instances exist, so\nbounds checking is not possible (in this *generic* function).\n`readFloat` uses to `Text.Read.Lex.numberToRational` which, among\nother things, calculates `10 ^ exponent`, which seems to take linear\ntime and memory.\n\n**Mitigation:** use `read`.  The `Read` instances for `Float` and\n`Double` perform bounds checks on the exponent, via\n`Text.Read.Lex.numberToRangedRational`.\n\n\n## In *toml-reader*\n\nThe issue was detected in *toml-reader* version 0.1.0.0, and\nmitigated in version 0.2.0.0 by immediately returning `Infinity`\nwhen the exponent is large enough that there\u0027s no reason to process\nit.\n",
  "id": "HSEC-2023-0007",
  "modified": "2025-11-14T14:45:34Z",
  "published": "2025-11-14T14:45:34Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://gitlab.haskell.org/ghc/ghc/-/issues/23538"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/brandonchinn178/toml-reader/issues/8"
    },
    {
      "type": "FIX",
      "url": "https://github.com/brandonchinn178/toml-reader/pull/9"
    }
  ],
  "schema_version": "1.5.0",
  "summary": "readFloat: memory exhaustion with large exponent"
}