### Problem
Scrapy’s `S3DownloadHandler` sends signed S3 requests over plaintext HTTP by default.
A normal request like `s3://bucket/key` is converted into `http://bucket.s3.amazonaws.com/key` unless `request.meta["is_secure"]` is explicitly set. The generated request is then signed with configured AWS credentials, so AWS authorization material can be sent without TLS.
Vulnerable code in `scrapy/core/downloader/handlers/s3.py`:
```python
scheme = "https" if request.meta.get("is_secure") else "http"
url = f"{scheme}://{bucket}.s3.amazonaws.com{path}"
```
The request is then signed and dispatched:
```python
self._signer.add_auth(awsrequest)
request = request.replace(url=url, headers=awsrequest.headers.items())
```
### Impact
Users making Scrapy `s3://` requests with AWS credentials are impacted.
A network attacker able to observe traffic between Scrapy and S3, such as a public Wi-Fi attacker, compromised router, ISP/corporate network observer, or local network attacker using ARP spoofing, can read:
```text
bucket/key path
AWS Authorization header
X-Amz-Security-Token, if temporary credentials are used
S3 object contents
S3 response headers
```
An active MITM attacker can also modify the plaintext S3 response body, status code, and headers before Scrapy processes it. This can cause scraped data poisoning, poisoned exports, HTTP cache poisoning when cache is enabled, and influence over later crawl targets through forged redirects or attacker-controlled links.
Suggested classification: **CWE-319: Cleartext Transmission of Sensitive Information**.
### PoC
A minimal PoC creates an `s3://` request, enables fake AWS settings, captures the request produced by `S3DownloadHandler`, and prints the rewritten URL and auth headers.
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.