CVE-2026-45820: 101arrowz Fflate

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

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 products

• 101arrowz Fflate: up to and including 0.8.2

Published 2026-07-22. Last modified 2026-08-19.