---
id: GHSA-p634-w6r4-rjp2
title: >-
  adm-zip: Duplicate ZIP entry names: getEntry() and extractAllTo() resolve to
  different content
summary: >-
  adm-zip: Duplicate ZIP entry names: getEntry() and extractAllTo() resolve to
  different content
severity: medium
cvss: 5.9
cwe:
  - CWE-436
  - CWE-696
vendor: adm-zip
product: adm-zip
ecosystem: npm
affected:
  - adm-zip <= 0.6.0
patched:
  - adm-zip 0.6.1
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T23:11:04Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-p634-w6r4-rjp2'
references:
  - url: >-
      https://github.com/cthackers/adm-zip/security/advisories/GHSA-p634-w6r4-rjp2
  - url: >-
      https://github.com/cthackers/adm-zip/commit/05101d47b3b983b705cc3e66fc34366118ba7b99
  - url: 'https://github.com/cthackers/adm-zip/releases/tag/v0.6.1'
  - url: 'https://github.com/advisories/GHSA-p634-w6r4-rjp2'
tags:
  - ghsa
  - npm
ingestedAt: '2026-09-29T23:52:50.541Z'
---

## Overview

### Summary

A 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.

### Details
- `zipFile.js:58-83` retains both entries in `entryList` but overwrites `entryTable[name]` with only the last one written.
- `adm-zip.js:83-95,658-663` uses `entryTable` for `getEntry()` lookups — returns the *last* duplicate.
- `adm-zip.js:769-914` iterates `entryList` for extraction — writes the *first* duplicate (sync, default overwrite policy).


### PoC
```js
const AdmZip = require('adm-zip');
const z = new AdmZip({ noSort: true });
z.addFile('a.txt', Buffer.from('FIRST'));
z.addFile('b.txt', Buffer.from('SECOND'));
const raw = Buffer.from(z.toBuffer());
// rename the a.txt entry to b.txt directly in the raw bytes
for (let at = raw.indexOf('a.txt'); at >= 0; at = raw.indexOf('a.txt', at + 5)) {
  raw.write('b.txt', at);
}
const parsed = new AdmZip(raw, { noSort: true });
const validated = parsed.getEntry('b.txt').getData().toString();
parsed.extractAllTo(outDir, false);
// validated === "SECOND", but the file written to disk === "FIRST"
```

Reproduced on the pinned commit (`2b4d84087d45344643e0183756e19191d52815cc`)

### Impact
An 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.

## Affected packages

- `adm-zip <= 0.6.0`

## Remediation

Upgrade to a patched release:

- `adm-zip 0.6.1`