Resource exhaustion in 101arrowz Fflate

CVE-2026-45820

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.

Vulnerability class: DoS (Denial of Service)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.003 (20.4th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 20th percentile — 20.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-45820: held from 0.005 to 0.003.

EPSS over last 30 days · oldest: 0.005 · newest: 0.003 · change: -0.002

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-45820?
CVE-2026-45820 is a high-severity vulnerability in 101arrowz Fflate, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-07-22.
How severe is CVE-2026-45820?
High severity. CVSS v3 base score is 7.5 out of 10.