CVE-2026-63311

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).

CVSS v3 5.3 MEDIUM

5.3^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 3.9 / Impact : 1.4

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact LOW

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/nltk/nltk/security/advisories/GHSA-3gqm-fcw5-w839	Exploit Mitigation Vendor Advisory
https://www.vulncheck.com/advisories/nltk-before-ssrf-via-dns-resolution-failure	Third Party Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*

History

14 Oct 2026, 13:10

Type	Values Removed	Values Added
Summary		(es) NLTK anterior a 3.10.0 (versiones afectadas menor o igual que 3.9.4) contiene una vulnerabilidad de falsificación de petición del lado del servidor (SSRF) en la función validate_network_url() en nltk/pathsec.py. La función auxiliar _resolve_hostname() captura OSError y ValueError durante socket.getaddrinfo() y devuelve una lista vacía; cuando la resolución DNS falla, el bucle de validación no ejecuta comprobaciones de IP y la función falla abierta, permitiendo que urlopen() proceda sin validación. Un atacante que puede desencadenar fallos de resolución DNS o usar el reenlace DNS puede eludir las protecciones SSRF y alcanzar recursos de red restringidos, incluyendo puntos finales de metadatos en la nube (p. ej., 169.254.169.254).

Information

Published : 2026-08-22 15:16

Updated : 2026-10-14 13:10

NVD link : CVE-2026-63311

Mitre link : CVE-2026-63311

CVE.ORG link : CVE-2026-63311

JSON object : View

Products Affected

nltk

nltk

CWE

CWE-918

Server-Side Request Forgery (SSRF)

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