The vulnerability stems from the parse_sitemap method's inability to detect and prevent parsing of a sitemap that refers to itself, leading to infinite recursion. This flaw can be exploited by an attacker by crafting a sitemap that includes a URL pointing to its own location. When the SitemapLoader attempts to parse this sitemap, it enters an infinite loop, consuming server resources and eventually crashing the Python process due to reaching the maximum recursion depth.

An attacker crafts a malicious sitemap (infinite-loop.xml) containing a URL that points to the sitemap itself. The attacker then hosts this sitemap on a server and triggers the vulnerable application to parse this sitemap by making a request to the application's endpoint that initiates sitemap loading. The application's attempt to parse the malicious sitemap results in infinite recursion, leading to resource exhaustion and a Denial-of-Service condition.

All users of the langchain-ai/langchain project who utilize the SitemapLoader class for parsing sitemaps are affected by this vulnerability. This includes applications that automatically parse sitemaps from untrusted sources.