# adm-zip duplicate ZIP entry name validation bypass

Source: https://junglewise.ai/threats/adm-zip-duplicate-zip-entry-names-getentry-and-extractallto-resolve-to-42f08f8e  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-29. Updated: 2026-09-30  
License: CC BY 4.0 with a link back

Severity: medium · CVSS 5.9 · Published 2026-09-29

adm-zip is a Node.js library for reading and writing ZIP archives. A malicious ZIP file containing duplicate entry names can be crafted so that entry validation via getEntry() approves one file's content, while extraction writes different bytes to disk under that name. An application that validates archive contents before extraction can be deceived into approving untrusted files.

Technologies: [adm-zip (npm)](https://junglewise.ai/threats/technologies/adm-zip). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Medium severity, with a CVSS score of 5.9, published 29 September 2026.

**Which products and versions are affected?** adm-zip (npm) <= 0.6.0.

**Is there a fix for This vulnerability?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run adm-zip (npm) or Adm-Zip at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability stems from inconsistent handling of duplicate ZIP entry names: the entryTable lookup table retains only the last duplicate, while entryList retains all entries. The getEntry() method consults entryTable and returns the last-written duplicate, but extractAllTo() iterates entryList and writes the first duplicate, creating a check/use split. An attacker supplies a ZIP with two entries sharing the same name, causing validation and extraction to resolve to different file contents.

## Affected products

- adm-zip

## Timeline

- 2026-09-29: disclosed

## Related threats

- [Adm-zip incorrect permission assignment with keepOriginalPermission](https://junglewise.ai/threats/cve-2026-114105-adm-zip-before-0-6-1-contains-an-incorrect-permission-assignment)
- [adm-zip inconsistent entry resolution in ZIP extraction](https://junglewise.ai/threats/cve-2026-114104-adm-zip-before-0-6-1-contains-an-inconsistent-entry-resolution)
- [adm-zip permission bit extraction privilege escalation](https://junglewise.ai/threats/cve-2026-102282-adm-zip-extraction-preserves-suid-sgid-bits-from-untrusted-zips)
- [adm-zip getDataAsync() decompression bomb bypass](https://junglewise.ai/threats/adm-zip-getdataasync-bypasses-the-maxoutputlength-size-guard-enforced-3e032cd1)
- [adm-zip async decompression denial of service](https://junglewise.ai/threats/adm-zip-unhandled-error-event-in-async-deflate-decompression-crashes-337da7e4)