{"id":"CVE-2026-114104","aliases":["GHSA-p634-w6r4-rjp2"],"url":"https://o3.security/vulnerability/CVE-2026-114104","summary":"adm-zip before 0.6.1 Duplicate ZIP Entry Name Validation Bypass","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.","published":"2026-10-21T00:37:05.291Z","modified":"2026-10-24T02:49:30.533624072Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"adm-zip","fixedVersion":"0.6.1"}],"fix":{"url":"https://github.com/cthackers/adm-zip/commit/05101d47b3b983b705cc3e66fc34366118ba7b99","label":"cthackers/adm-zip@05101d4"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/114xxx/CVE-2026-114104.json"},{"type":"ADVISORY","url":"https://github.com/cthackers/adm-zip/security/advisories/GHSA-p634-w6r4-rjp2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-114104"},{"type":"ADVISORY","url":"https://www.vulncheck.com/advisories/adm-zip-before-0.6.1-duplicate-zip-entry-name-validation-bypass"},{"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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T02:49:30.533624072Z"}}