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CVE-2026-70626— NLTK before 3.9.4 Symlink Escape via CorpusReader

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。 NLTK 3.9.4之前版本存在后置链接漏洞，该漏洞源于CorpusReader.open()的路径验证是词法上的且未考虑符号链接解析，可能导致本地攻击者读取语料库根目录之外的任意文件。

CVSS 6.2 · Medium EPSS 0.20% · P9

Possible ATT&CK Techniques 1 AI

T1083 · File and Directory Discovery

Affected Version Matrix 2

VendorProduct Version RangeStatus
nltk nltk < 3.9.4 affected
3.9.4 unaffected
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I. Basic Information for CVE-2026-70626

Vulnerability Information
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Vulnerability Title
NLTK before 3.9.4 Symlink Escape via CorpusReader
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK versions before 3.9.4 contain a symlink escape vulnerability in CorpusReader.open() that allows local attackers to read arbitrary files outside the corpus root. The vulnerability exists because path validation is lexical and does not account for symlink resolution, enabling attackers to place symlinks inside the corpus root to access files outside the intended boundary.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在文件访问前对链接解析不恰当(链接跟随)
Source: CVE Program / CVE List V5
Vulnerability Title
NLTK 后置链接漏洞
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。 NLTK 3.9.4之前版本存在后置链接漏洞，该漏洞源于CorpusReader.open()的路径验证是词法上的且未考虑符号链接解析，可能导致本地攻击者读取语料库根目录之外的任意文件。
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 ~ 3.9.4 -

II. Public POCs for CVE-2026-70626

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III. Intelligence Information for CVE-2026-70626

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Vendor Advisories for CVE-2026-70626 (2)

Same Patch Batch · nltk · 2026-08-22 · 11 CVEs total

CVE-2026-71513 8.8 HIGH NLTK 3.10.0 through 3.10.2 Remote Code Execution via AllowlistUnpickler Dotted-Name Bypass
CVE-2026-62388 7.5 HIGH NLTK before 3.10.0 Insecure Default Configuration in pathsec.py
CVE-2026-62384 7.5 HIGH NLTK FramenetCorpusReader Symlink Sandbox Bypass before 3.10.2
CVE-2026-66393 7.5 HIGH NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder
CVE-2026-63312 7.5 HIGH NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read
CVE-2026-65915 6.5 MEDIUM NLTK before 3.10.0 Arbitrary File Read via FileSystemPathPointer
CVE-2026-62385 5.9 MEDIUM NLTK 3.9.4 Path Traversal via FrameNet and NKJP Readers
CVE-2026-62383 5.5 MEDIUM nltk IPIPANCorpusReader Symlink Arbitrary File Read
CVE-2026-63311 5.3 MEDIUM NLTK before 3.10.0 SSRF via DNS Resolution Failure
CVE-2026-71514 2.5 LOW NLTK 3.9.4 through 3.10.2 Path Traversal via CrubadanCorpusReader pathsec Bypass

IV. Related Vulnerabilities

Same product: nltk
Same vendor: nltk
Same weakness: CWE-59

V. Comments for CVE-2026-70626

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