Scrapy versions up to 2.13.2 are vulnerable to a denial of service (DoS) attack due to a flaw in its brotli decompression implementation. The protection mechanism against decompression bombs fails to mitigate the brotli variant, allowing remote servers to crash clients with less than 80GB of available memory. This occurs because brotli can achieve extremely high compression ratios for zero-filled data, leading to excessive memory consumption during decompression.
Scrapy 1.4 allows remote attackers to cause a denial of service (memory consumption) via large files because arbitrarily many files are read into memory, which is especially problematic if the files are then individually written in a separate thread to a slow storage resource, as demonstrated by interaction between dataReceived (in core/downloader/handlers/http11.py) and S3FilesStore.