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CVE-2026-66393— NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder

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.

NLTK 3.9.4 之前的版本中存在一个无界递归漏洞，位于 函数中。攻击者可以通过构造深层嵌套的 JSON 结构，导致拒绝服务（DoS）攻击。攻击者可以构造超出递归限制深度的 JSON 有效载荷，从而触发未处理的 ，导致 Python 进程崩溃。

CVSS 7.5 · High EPSS 0.49% · P40

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

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-2026-66393

Vulnerability Information
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Vulnerability Title
NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.
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:H
Source: CVE Program / CVE List V5
Vulnerability Type
未经控制的递归
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
nltk nltk 0 ~ 3.9.4 -

II. Public POCs for CVE-2026-66393

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 7561 chars
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III. Intelligence Information for CVE-2026-66393

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Vendor Advisories for CVE-2026-66393 (2)

Same Patch Batch · nltk · 2026-08-22 · 12 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 pathsec
CVE-2026-62384 7.5 HIGH NLTK FramenetCorpusReader Symlink Sandbox Bypass before 3.10.2
CVE-2026-63312 7.5 HIGH NLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read
CVE-2026-63310 7.1 HIGH NLTK before 3.9.3 Missing Post-Download Integrity Verification
CVE-2026-65915 6.5 MEDIUM NLTK before 3.10.0 Arbitrary File Read via FileSystemPathPointer
CVE-2026-70626 6.2 MEDIUM NLTK before 3.9.4 Symlink Escape via CorpusReader
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-674

V. Comments for CVE-2026-66393

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