CVE-2026-12259

In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction REQUIRED

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d	Permissions Required

Configurations

Configuration 1 (hide)

cpe:2.3:a:nltk:nltk:3.9.4:*:*:*:*:*:*:*

History

23 Oct 2026, 22:10

Type	Values Removed	Values Added
Summary		(es) En la versión 3.9.4 de nltk, la función “nltk.downloader.Downloader._download_package()” escribe los bytes del paquete descargado en el disco y puede extraerlos antes de aplicar la validación de suma de comprobación SHA-256 o MD5. Esto permite a un atacante manipular el cuerpo de la respuesta del paquete para “info.url” a través de un espejo comprometido, un proxy malicioso u otra condición de sustitución de origen, lo que lleva a la instalación de bytes de paquete controlados por el atacante. La vulnerabilidad puede resultar en que contenido malicioso de corpus o modelo sea confiado por usuarios o aplicaciones posteriores.

15 Oct 2026, 19:21

Type	Values Removed	Values Added
References	~~() https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d -~~	() https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d - Permissions Required
CPE		cpe:2.3:a:nltk:nltk:3.9.4:::::::*
First Time		Nltk Nltk nltk
CVSS	v2 : ~~unknown~~ v3 : ~~5.3~~	v2 : unknown v3 : 6.5

Information

Published : 2026-08-03 08:17

Updated : 2026-10-23 22:10

NVD link : CVE-2026-12259

Mitre link : CVE-2026-12259

CVE.ORG link : CVE-2026-12259

JSON object : View

Products Affected

nltk

nltk

CWE

CWE-494

Download of Code Without Integrity Check

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