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CVE-2026-78682— NLTK before 3.10.3 SSRF Protection Bypass via Proxy

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 3.10.3之前版本存在服务端请求伪造漏洞，该漏洞源于在配置HTTP代理时，nltk.pathsec.urlopen及调用者nltk.data.load、nltk.downloader.Downloader.index/download对目标主机名验证不足，导致代理可能将请求转发至内部回环服务，攻击者利用此漏洞可泄露内部HT

CVSS 7.5 · High EPSS 0.43% · P36

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-2026-78682

Vulnerability Information
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Vulnerability Title
NLTK before 3.10.3 SSRF Protection Bypass via Proxy
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK before 3.10.3 contains a server-side request forgery vulnerability in nltk.pathsec.urlopen (and callers nltk.data.load, nltk.downloader.Downloader.index/download) when an HTTP proxy is configured. pathsec.urlopen validates the requested hostname locally, but proxy-handler inheritance disables the safe HTTP/HTTPS handlers so the actual fetch is performed by the proxy against a destination that is never re-validated. An attacker can supply a validated public URL that the proxy forwards to an internal loopback-only service, allowing disclosure of internal HTTP resources, loading of forged downloader indexes, and installation of attacker-chosen package content.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5
Vulnerability Title
Natural Language Toolkit 服务端请求伪造漏洞
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之前版本存在服务端请求伪造漏洞，该漏洞源于在配置HTTP代理时，nltk.pathsec.urlopen及调用者nltk.data.load、nltk.downloader.Downloader.index/download对目标主机名验证不足，导致代理可能将请求转发至内部回环服务，攻击者利用此漏洞可泄露内部HT
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-2026-78682

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Reproduced successfully in a real sandbox · Below is the actual recording of building the environment and exploiting the vulnerability.
Success marker: VULNERABLE: internal loopback resource exfiltrated -- fetched PROOF_0f4375b9e3b5ba5d through attacker proxy (destination 127.0.0.1 never re-validated)
Reproduction recording is a Pro+ exclusive
Watch the full sandbox build + live exploit recording for this CVE. Limited-time ¥499/mo.
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claude_code · 11164 chars
GitHub 复现环境（可 clone 直接跑）
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III. Intelligence Information for CVE-2026-78682

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Vendor Advisories for CVE-2026-78682 (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-2026-78683 9.6 CRITICAL NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
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-2026-79676 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-918

V. Comments for CVE-2026-78682

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