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CVE-2026-78683— NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

Quick assessment

Affected
nltk nltk
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Natural Language Toolkit是Natural Language Toolkit组织开源的一个自然语言处理工具包。 Natural Language Toolkit 3.10.0之前版本存在反序列化注入漏洞，该漏洞源于nltk/parse/transitionparser.py文件中的TransitionParser.parse()方法存在不安全的pickle反序列化，未覆盖find_class()，允许任意类解析，攻击者可通过加载特制模型文件执行任意Python代码。

CVSS 9.6 · Critical EPSS 0.51% · P42

Possible ATT&CK Techniques 1 AI

T1210 · Exploitation of Remote Services

Affected Version Matrix 2

VendorProduct Version RangeStatus
nltk nltk < 3.10.0 affected
3.10.0 unaffected
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I. Basic Information for CVE-2026-78683

Vulnerability Information
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Vulnerability Title
NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
可信数据的反序列化
Source: CVE Program / CVE List V5
Vulnerability Title
Natural Language Toolkit 反序列化注入漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Natural Language Toolkit是Natural Language Toolkit组织开源的一个自然语言处理工具包。 Natural Language Toolkit 3.10.0之前版本存在反序列化注入漏洞，该漏洞源于nltk/parse/transitionparser.py文件中的TransitionParser.parse()方法存在不安全的pickle反序列化，未覆盖find_class()，允许任意类解析，攻击者可通过加载特制模型文件执行任意Python代码。
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 0 ~ 3.10.0 -

II. Public POCs for CVE-2026-78683

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7790 chars
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III. Intelligence Information for CVE-2026-78683

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Vendor Advisories for CVE-2026-78683 (2)

Same Patch Batch · nltk · 2026-08-25 · 8 CVEs total

CVE-2026-79657 9.8 CRITICAL NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization
CVE-2026-79675 9.8 CRITICAL NLTK before 3.10.3 JVM Argument Injection via Per-Call Options
CVE-2026-79674 8.2 HIGH NLTK 3.10.2 Path Traversal via corpus-reader constructors
CVE-2026-78680 7.8 HIGH NLTK before 3.10.3 Arbitrary Code Execution via Graphviz dot Binary
CVE-2026-78681 7.5 HIGH NLTK before 3.10.3 Entity Expansion DoS via ElementTree
CVE-2026-78682 7.5 HIGH NLTK before 3.10.3 SSRF Protection Bypass via Proxy
CVE-2026-79676 5.9 MEDIUM NLTK before 3.10.3 Path Traversal via Symlink Bypass

IV. Related Vulnerabilities

Same product: nltk
Same vendor: nltk
Same weakness: CWE-502

V. Comments for CVE-2026-78683

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