CVE-2026-78682: Nltk

High severity, CVSS 7.5. EPSS: 0.4% chance of exploitation in the next 30 days.

NLTK before 3.10.3 contains a server-side request forgery vulnerability in nltk.pathsec.urlopen (and callers nltk.data.load, nltk.downloader.Downloader.index/download) when an HTTP proxy is configured. pathsec.urlopen validates the requested hostname locally, but proxy-handler inheritance disables the safe HTTP/HTTPS handlers so the actual fetch is performed by the proxy against a destination that is never re-validated. An attacker can supply a validated public URL that the proxy forwards to an internal loopback-only service, allowing disclosure of internal HTTP resources, loading of forged downloader indexes, and installation of attacker-chosen package content.

Affected products

• Nltk Nltk: before 3.10.3 (fixed in 3.10.3)

Published 2026-08-25. Last modified 2026-10-08.