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CVE-2026-63311 Details

Description

NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:5.3 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839	[email protected]	ExploitMitigationVendor Advisory
https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure	[email protected]	Third Party Advisory

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-918	Server-Side Request Forgery (SSRF)	[email protected]

Affected Products

Product	Versions
nltk nltk	< 3.10.0
CPE cpe:2.3:a:nltk:nltk:::::::: Remediation No remediation found in references.

Change History

4 change records found show changes

Date	Action	Recorded By
Aug 27, 2026	Initial Analysis	[email protected]
Aug 26, 2026	CVE Modified	[email protected]
Aug 26, 2026	CVE Modified	CISA-ADP
Aug 22, 2026	New CVE Received	[email protected]