Vulnerability · Published Jul 22, 2026 · Assigned by seal

CVE-2026-45820

Medium 6.6

In plain English

A medium-severity infinite loop in fflate from 101arrowz. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)6.6Medium

Exploit odds (30 days)0.3%top 79.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	fflate	0.4.9	GHSA-px8p-9vwx-vf98
npm	fflate	0.5.4	GHSA-px8p-9vwx-vf98
npm	fflate	0.6.11	GHSA-px8p-9vwx-vf98
npm	fflate	0.7.5	GHSA-px8p-9vwx-vf98
npm	fflate	0.8.3	GHSA-px8p-9vwx-vf98

Affected products (as reported)

Vendor	Product	Versions
101arrowz	fflate	0.4.5 – through 0.4.80.5.0 – through 0.5.30.6.0 – through 0.6.100.7.0 – through 0.7.40.8.0 – through 0.8.2

Weakness: CWE-835, CWE-400 · 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/E:U/S:N/AU:Y/R:U/V:D/RE:M/U:Amber

In plain English

Official description

Affected packages & fixed versions

Affected products (as reported)

References