Scrapy is a high-level web crawling and scraping framework for Python. From 1.4.0 until 2.14.2, RefererMiddleware in scrapy/spidermiddlewares/referer.py treated a Referrer-Policy response-header value that resembled a Python import path as a referrer policy class, imported the referenced object, and called it. A malicious website could supply a callable such as sys.exit and terminate a crawler processing the response. This issue is fixed in version 2.14.2.

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.