SSRF in Nltk
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.
Vulnerability class: SSRF (Server-Side Request Forgery)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (35.8th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/nltk/nltk/security/advisories/GHSA-6ww7-3frv-cqxh (Exploit, vendor-advisory, Vendor Advisory)
- www.vulncheck.com/advisories/nltk-before-ssrf-protection-bypass-via-proxy (Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-78682?
- CVE-2026-78682 is a high-severity vulnerability in Nltk, classified under Server-Side Request Forgery (SSRF). CVSS score: 7.5/10. Published 2026-08-25.
- How severe is CVE-2026-78682?
- High severity. CVSS v3 base score is 7.5 out of 10.