CVE-2026-78682

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.

CVSS 4.0

8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS

0.4% chance of exploitation in the next 30 days; higher than 37% of CVEs (scores of 2026-10-25)

CWE

CWE-918

Published

2026-08-25

Modified

2026-10-12

Record from

the NVD, synced 2026-10-19

Affected

• nltk:nltk

Packages (OSV)

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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