GHSA-p634-w6r4-rjp2: adm-zip Duplicate ZIP Entry Names: GetEntry() Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-p634-w6r4-rjp2",
  "modified" : "2026-09-29T23:11:01Z",
  "published" : "2026-09-29T23:11:01Z",
  "aliases" : [ ],
  "summary" : "adm-zip: Duplicate ZIP entry names: getEntry() and extractAllTo() resolve to different content",
  "details" : "### Summary\n\nA ZIP file can contain two entries with the identical name. adm-zip keeps both in its internal entry list, but its name-lookup table only retains the last one written. `getEntry(name)` and `extractAllTo()` walk these two different internal structures, so they can each resolve a duplicate name to a *different* entry. An application that validates a named entry's contents via `getEntry()` before trusting an archive, then extracts the whole archive, can end up approving one file's content while a different file's bytes are what actually land on disk under that name.\n\n### Details\n- `zipFile.js:58-83` retains both entries in `entryList` but overwrites `entryTable[name]` with only the last one written.\n- `adm-zip.js:83-95,658-663` uses `entryTable` for `getEntry()` lookups — returns the *last* duplicate.\n- `adm-zip.js:769-914` iterates `entryList` for extraction — writes the *first* duplicate (sync, default overwrite policy).\n\n\n### PoC\n```js\nconst AdmZip = require('adm-zip');\nconst z = new AdmZip({ noSort: true });\nz.addFile('a.txt', Buffer.from('FIRST'));\nz.addFile('b.txt', Buffer.from('SECOND'));\nconst raw = Buffer.from(z.toBuffer());\n// rename the a.txt entry to b.txt directly in the raw bytes\nfor (let at = raw.indexOf('a.txt'); at >= 0; at = raw.indexOf('a.txt', at + 5)) {\n  raw.write('b.txt', at);\n}\nconst parsed = new AdmZip(raw, { noSort: true });\nconst validated = parsed.getEntry('b.txt').getData().toString();\nparsed.extractAllTo(outDir, false);\n// validated === \"SECOND\", but the file written to disk === \"FIRST\"\n```\n\nReproduced on the pinned commit (`2b4d84087d45344643e0183756e19191d52815cc`)\n\n### Impact\nAn application that checks a named entry's content before trusting an untrusted ZIP, then extracts it, can be made to approve different bytes than what actually gets written to disk — the classic check/use split that this kind of validate-then-extract pattern relies on.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "adm-zip"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.6.1"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 0.6.0"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/cthackers/adm-zip/security/advisories/GHSA-p634-w6r4-rjp2"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cthackers/adm-zip/commit/05101d47b3b983b705cc3e66fc34366118ba7b99"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/cthackers/adm-zip"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/cthackers/adm-zip/releases/tag/v0.6.1"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-436", "CWE-696" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-29T23:11:01Z",
    "nvd_published_at" : null
  }
}