CVE-2026-63311

MEDIUM 5.3

NLTK before 3.10.0 SSRF via DNS Resolution Failure

CVSS Score

5.3

EPSS Score

0.0%

EPSS Percentile

0th

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).

CWE	CWE-918
Vendor	nltk
Product	nltk
Published	Aug 22, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

Low

Availability

None

Affected Versions

nltk / nltk

0 < 3.10.0

References

NVD ↗ CVE.org ↗ EPSS Data ↗

github.com: https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839 vulncheck.com: https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure