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CVE-2026-81724— NLTK before 3.10.3 Denial of Service via Uncontrolled Recursion

Quick assessment

Affected
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.

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 3.10.3之前版本存在资源管理错误漏洞，该漏洞源于nltk.featstruct.FeatStructReader存在不受控制的递归问题，可能导致未经身份验证的攻击者通过提供深度嵌套的特征结构输入，造成拒绝服务。

CVSS 5.3 · Medium EPSS 0.46% · P38

Affected Version Matrix 2

VendorProduct Version RangeStatus
nltk nltk < 3.10.3 affected
3.10.3 unaffected
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I. Basic Information for CVE-2026-81724

Vulnerability Information
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Vulnerability Title
NLTK before 3.10.3 Denial of Service via Uncontrolled Recursion
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未经控制的递归
Source: CVE Program / CVE List V5
Vulnerability Title
Natural Language Toolkit 资源管理错误漏洞
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 3.10.3之前版本存在资源管理错误漏洞，该漏洞源于nltk.featstruct.FeatStructReader存在不受控制的递归问题，可能导致未经身份验证的攻击者通过提供深度嵌套的特征结构输入，造成拒绝服务。
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 ~ 3.10.3 -

II. Public POCs for CVE-2026-81724

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III. Intelligence Information for CVE-2026-81724

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Vendor Advisories for CVE-2026-81724 (2)

Same Patch Batch · nltk · 2026-08-27 · 6 CVEs total

CVE-2026-81722 7.5 HIGH nltk PorterStemmer before 3.10.3 Quadratic-time DoS
CVE-2026-81727 7.1 HIGH NLTK before 3.10.3 Hardlink File Overwrite via downloader
CVE-2026-81726 7.0 HIGH NLTK through 3.10.3 Path Traversal via Model-Artifact APIs
CVE-2026-81723 3.7 LOW NLTK before 3.10.3 Quadratic CPU Exhaustion via XMLCorpusView
CVE-2026-81725 3.7 LOW NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader

IV. Related Vulnerabilities

Same product: nltk
Same vendor: nltk
Same weakness: CWE-674

V. Comments for CVE-2026-81724

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