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.