# CVE-2026-78206: exceljs zip bomb denial of service

Source: https://junglewise.ai/threats/cve-2026-78206-exceljs-zip-bomb-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-24. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-78206 · Severity: high · CVSS 7.5 · Published 2026-08-24

exceljs is a popular Node.js library for reading and writing Excel workbooks. Versions through 4.4.0 fail to validate the size of decompressed data from xlsx archives, allowing attackers to upload specially crafted files that expand to gigabytes in memory and crash the application, disrupting service for all users.

## Quick answers

**Is CVE-2026-78206 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78206 being exploited in the wild.

**How severe is CVE-2026-78206?** High severity, with a CVSS score of 7.5, published 24 August 2026.

**Which products and versions are affected?** exceljs exceljs through 4.4.0.

**Is there a fix for CVE-2026-78206?** 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 CVE-2026-78206 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-78206?** Check whether anything you run is named in the advisory. 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

This is a classic zip bomb vulnerability (CWE-409) affecting archive decompression. The vulnerability exists in exceljs's xlsx parsing logic, which decompresses all entries from a supplied archive into memory without enforcing limits on individual entry sizes, total decompressed size, or compression ratios. An attacker can craft a malicious xlsx file containing highly compressed payloads (e.g., a 1MB file that decompresses to several GB) that, when processed by a server using exceljs, exhausts available memory and causes denial of service. The attack requires only the ability to upload or provide an xlsx file to a system using the affected library; no authentication or special privileges are needed if file uploads are publicly available. Patches should implement decompression limits or stream-based processing to prevent memory exhaustion.

## Affected products

- exceljs exceljs through 4.4.0

## Timeline

- 2026-08-24: disclosed
- other: CVE-2026-78206 assigned

## References

- [https://www.npmjs.com/package/exceljs](https://www.npmjs.com/package/exceljs)
- [https://github.com/exceljs/exceljs](https://github.com/exceljs/exceljs)