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Miggo AIRoot Cause AnalysisThe vulnerability, identified as a Server-Side Request Forgery (SSRF) (CWE-918), stems from the nltk.pathsec.urlopen function's behavior when an HTTP proxy is configured. While nltk.pathsec.urlopen performed local hostname validation, this validation was insufficient because the actual network request was then handed off to a proxy. The proxy, not being subject to NLTK's internal validation, could be tricked into forwarding the request to an internal or unauthorized destination, bypassing the intended security controls. This allowed for the disclosure of internal HTTP resources, loading of forged downloader indexes, and installation of attacker-chosen package content.
The core fix, as evidenced by commit 767333a005a1cd3d82d2029215f2dbe66a5844d9, directly addresses this flaw in nltk.pathsec.urlopen. The patch introduces a new mechanism (_reject_unpinnable_proxied_fetch) that explicitly refuses proxied fetches by default when ENFORCE is true, unless the operator explicitly opts in to trust the proxy. This ensures that NLTK no longer proceeds with requests whose egress destination cannot be fully validated.
The functions nltk.data.load, nltk.downloader.Downloader.index, and nltk.downloader.Downloader.download are identified as vulnerable because they are direct or indirect callers of nltk.pathsec.urlopen. Therefore, any exploitation of the SSRF vulnerability would involve these functions initiating a network request that ultimately flows through the vulnerable nltk.pathsec.urlopen when a proxy is configured. The patch to nltk.pathsec.urlopen effectively mitigates the vulnerability for all these calling functions by addressing the root cause at the point of network request execution.
nltk.pathsec.urlopennltk/pathsec.py
nltk.data.loadnltk/data.py
nltk.downloader.Downloader.indexnltk/downloader.py
nltk.downloader.Downloader.downloadnltk/downloader.py
| Package Name | Ecosystem | Vulnerable Versions | First Patched Version |
|---|---|---|---|
| nltk | pip | <= 3.10.2 |