What’s Vulnerable › Vulnerabilities

CVE-2026-78682: NLTK before 3.10.3 SSRF Protection Bypass via Proxy

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-25 · updated 2026-10-12
• Weakness: CWE-918

Description

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: before 3.10.3 — fixed in 3.10.3

How to fix

Upgrade to a fixed version: nltk 3.10.3. Check the vendor advisory for mitigations.

References

• https://github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh
• https://www.vulncheck.com/advisories/nltk-before-ssrf-protection-bypass-via-proxy
• https://github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh

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