fflate unzipSync can enter an infinite loop when parsing malformed ZIP64 archives
fflate through 0.8.2 is vulnerable to denial of service via an infinite loop in unzipSync(). A crafted ZIP archive with a central directory entry declaring compressed_size=0xFFFFFFFF (ZIP64 sentinel) but missing the required ZIP64 extra field tag 0x0001 causes z64e() to loop indefinitely due to out-of-bounds reads returning undefined, which coerces to 0, keeping the loop condition permanently true.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | fflate | >= 0.4.5, < 0.4.9, >= 0.5.0, < 0.5.4, >= 0.6.0, < 0.6.11, >= 0.7.0, < 0.7.5, >= 0.8.0, < 0.8.3 | 0.4.9, 0.5.4, 0.6.11, 0.7.5, 0.8.3 |
References
- https://nvd.nist.gov/vuln/detail/CVE-2026-45820
- https://github.com/101arrowz/fflate/commit/e6d5e6e1076892f72770ac732d83c81da9f3316e
- https://github.com/101arrowz/fflate
- https://github.com/101arrowz/fflate/blob/f7873560ad229c22c4b23b06c6a3806ffde77569/src/index.ts#L2714
- https://github.com/101arrowz/fflate/releases/tag/v0.8.3
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-400- Platform
- npm
- Package
fflate- Disclosed
- 22.07.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-px8p-9vwx-vf98 - CC BY 4.0
Vulnerability history: fflate
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
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