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CVE-2026-12259— Improper Input Validation in nltk/nltk

Quick assessment

Affected
nltk nltk/nltk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

NLTK是NLTK组织开源的一个自然语言处理工具包。 NLTK 3.9.4版本存在软件供应链问题漏洞，该漏洞源于 函数在强制执行SHA-256或MD5校验和验证前将下载的包字节写入磁盘并可能解压，可能导致攻击者通过受损镜像或恶意代理篡改包响应，安装攻击者控制的包字节，使恶意语料库或模型内容被下游用户或应用信任。

AI Predicted 6.5 Difficulty: Moderate EPSS 0.14% · P3

Possible ATT&CK Techniques 1 AI

T1195 · Supply Chain Compromise

Affected Version Matrix 1

VendorProduct Version RangeStatus
nltk nltk/nltk unspecified≤ latest affected
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I. Basic Information for CVE-2026-12259

Vulnerability Information
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Vulnerability Title
Improper Input Validation in nltk/nltk
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
下载代码缺少完整性检查
Source: CVE Program / CVE List V5
Vulnerability Title
NLTK 软件供应链问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
NLTK是NLTK组织开源的一个自然语言处理工具包。 NLTK 3.9.4版本存在软件供应链问题漏洞，该漏洞源于`nltk.downloader.Downloader._download_package()`函数在强制执行SHA-256或MD5校验和验证前将下载的包字节写入磁盘并可能解压，可能导致攻击者通过受损镜像或恶意代理篡改包响应，安装攻击者控制的包字节，使恶意语料库或模型内容被下游用户或应用信任。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nltk nltk/nltk unspecified ~ latest -

II. Public POCs for CVE-2026-12259

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III. Intelligence Information for CVE-2026-12259

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Vendor Advisories for CVE-2026-12259 (1)

IV. Related Vulnerabilities

Same product: nltk/nltk
Same vendor: nltk
Same weakness: CWE-494

V. Comments for CVE-2026-12259

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