CVE-2026-104182: stream-json JSONC Parser And Verifier Re-scan Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-hqr4-qq8f-hg3x",
  "modified" : "2026-10-05T22:49:27Z",
  "published" : "2026-10-05T22:49:27Z",
  "aliases" : [ "CVE-2026-104182" ],
  "summary" : "stream-json: JSONC parser and verifier re-scan the whole accumulated comment on every input chunk",
  "details" : "## Summary\n\nThe JSONC parser (`stream-json/jsonc/parser.js`) and verifier (`stream-json/jsonc/verifier.js`) scan a comment for its terminator starting from the comment's opening `/` on every input chunk. When a comment doesn't finish inside the current buffer, the scanner returns the comment's start offset and the buffer keeps the whole comment, so the next chunk re-scans everything seen so far. A single comment of length n delivered across many chunks costs O(n²) CPU.\n\nThis is the same class as GHSA-528h-pc64-c93x (path filters, medium, CWE-407): an algorithmic-complexity re-scan in a streaming feature. It's a different code path though — the comment scanner in `handleComment`, which the 3.5.0 depth cap doesn't touch — so upgrading past that advisory doesn't help here. The plain JSON parser is fine: its strings and numbers advance and drop consumed bytes, and only comments retain and re-scan.\n\n## Proof of concept\n\n```\nnpm i stream-json@3.5.0\n```\n\n```js\nimport Parser from 'stream-json/jsonc/parser.js';\n\nfunction feed(N) {\n  return new Promise(resolve => {\n    const stream = Parser.asStream();            // default options\n    stream.on('data', () => {});\n    stream.on('error', () => {});\n    stream.on('end', resolve);\n    const doc = '/*' + 'a'.repeat(N) + '*/1';     // one valid, closed comment\n    for (let i = 0; i < doc.length; i += 16384)   // 16 KB pieces, as a socket delivers a body\n      stream.write(doc.slice(i, i + 16384));\n    stream.end();\n  });\n}\n```\n\nTiming the pipeline (Node 22, one core, clean install): a 2 MB comment blocks the event loop ~0.9 s, 4 MB ~2.9 s, 8 MB ~13 s — roughly 4x per doubling, so quadratic. Smaller chunks make it worse, and the attacker controls TCP segment size: a fixed 4 MB comment takes ~0.75 s at 64 KB chunks, ~2.8 s at 16 KB, ~11 s at 4 KB. Feeding the same input to the JSONC verifier reproduces it identically.\n\n## Impact\n\nRemote, unauthenticated CPU denial of service against any service that runs untrusted input through the JSONC parser or verifier: one request pins a core and stalls the whole event loop.\n\n## Caveat\n\nOnly the JSONC entry points are affected; an app on the default JSON parser is safe. The comment doesn't need to be malformed - a valid, properly closed comment does it. The payload is a few MB, or less if the client sends small chunks. I've suggested medium and left the CVSS vector to you.\n\n---\n\n# Maintainer note on scope\n\nThe attack vector is local — stream-json's documented input is data the user owns (JSONC is configuration you wrote); it is not designed for input from the open internet, and the docs now say so explicitly for JSONC. Comments now mirror chunked strings (`startComment` / `commentChunk` / `endComment`, packed `commentValue`); the scan resumes across input chunks, so a comment of any length costs linear time, and constant memory without packing.",
  "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" : "3.6.0"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 3.5.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/uhop/stream-json/security/advisories/GHSA-hqr4-qq8f-hg3x"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-104182"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uhop/stream-json/commit/c0299dc168ce9455ef5ca5b6a0f6850ee7fa0468"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/uhop/stream-json"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/uhop/stream-json/releases/tag/3.6.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-407" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-05T22:49:27Z",
    "nvd_published_at" : "2026-10-01T21:17:19Z"
  }
}