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.
NLTK 在 3.10.3 之前版本中存在一个不受控的递归漏洞，位于 中。未认证的攻击者可以通过提供深度嵌套的特征结构输入来触发拒绝服务（DoS）。攻击者可以构造包含超过 Python 递归限制的嵌套括号的简单载荷，从而引发未处理的 ，导致解析用户提供的特征结构或特征语法的进程崩溃。
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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
Affected Products
II. Public POCs for CVE-2026-81724
| # | POC Description | Source Link | Shenlong Link |
|---|
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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
-
CVE-2026-81727
NLTK before 3.10.3 Hardlink File Overwrite via downloader -
CVE-2026-81726
NLTK through 3.10.3 Path Traversal via Model-Artifact APIs -
CVE-2026-81725
NLTK before 3.10.3 Regular Expression Denial of Service via -
CVE-2026-81723
NLTK before 3.10.3 Quadratic CPU Exhaustion via XMLCorpusVie -
CVE-2026-81722
nltk PorterStemmer before 3.10.3 Quadratic-time DoS
Same vendor: nltk
-
CVE-2026-81727
NLTK before 3.10.3 Hardlink File Overwrite via downloader -
CVE-2026-81726
NLTK through 3.10.3 Path Traversal via Model-Artifact APIs -
CVE-2026-81725
NLTK before 3.10.3 Regular Expression Denial of Service via -
CVE-2026-81723
NLTK before 3.10.3 Quadratic CPU Exhaustion via XMLCorpusVie -
CVE-2026-81722
nltk PorterStemmer before 3.10.3 Quadratic-time DoS
Same weakness: CWE-674
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CVE-2026-16781
SVG File Parsing Stack Exhaustion Vulnerability in Autodesk -
CVE-2026-76098
Mistune has Denial of Service — RecursionError via Excessive -
CVE-2026-9769
justhtml before 1.10.0 Denial of Service via deeply nested H -
CVE-2026-66393
NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder -
CVE-2026-63462
Unleash: Unauthenticated single-request DoS via OpenAPI vali
V. Comments for CVE-2026-81724
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