GHSA-8823-qg2x-pv9f

## Gzip Decompression Bomb Bypasses Sitemap Size Limit ### Summary `ultimate-sitemap-parser` enforces a 100 MiB size limit on sitemap responses, but applies it only to the **compressed** bytes received over the network. When a `.gz` sitemap is fetched, `usp/helpers.py:239` calls `gzip_lib.decompress(data)` with no output-size cap, allowing an attacker-controlled server to serve a small gzip-compressed payload (~549 KB) that expands to over 120 MiB in process memory. This completely bypasses the declared limit and can exhaust memory or crash any process that calls `sitemap_tree_for_homepage()` against an untrusted site. ### Details The library declares a maximum sitemap size constant in `usp/fetch_parse.py:64`: ```python __MAX_SITEMAP_SIZE = 100 * 1024 * 1024 # Max. uncompressed sitemap size ``` Despite the comment saying "uncompressed", this value is passed directly to the HTTP client layer at `usp/fetch_parse.py:130`: ```python web_client.set_max_response_data_length(self.__MAX_SITEMAP_SIZE) ``` The HTTP client (`usp/web_client/requests_client.py:57-58`) slices only the raw compressed response bytes: ```python data = self.__requests_response.content[: self.__max_response_data_length] ``` The truncated (but still compressed) bytes are then passed through the pipeline to `usp/fetch_parse.py:175`: ```python response_content = ungzipped_response_content(url=self._url, response=response) ``` Inside `ungzipped_response_content` (`usp/helpers.py:265-267`), when the URL ends in `.gz` or the response carries a gzip content type, decompression is triggered: ```python if __response_is_gzipped_data(url=url, response=response): data = gunzip(data) ``` The `gunzip` function (`usp/helpers.py:239`) decompresses without any output-size guard: ```python gunzipped_data = gzip_lib.decompress(data) ``` No post-decompression size check exists anywhere in the call chain. Dynamic reproduction confirmed that 549,213 bytes of compressed input passed the 100 MiB gate che