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CVE-2026-63311— NLTK before 3.10.0 SSRF via DNS Resolution Failure

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 3.10.0 之前的版本（受影响版本为 <= 3.9.4）中， 文件中的 函数存在服务器端请求伪造（SSRF）漏洞。 该函数内部的 辅助函数在调用 时捕获了 和 异常，并返回一个空列表。当 DNS 解析失败时，验证循环中不会执行任何 IP 检查，导致函数“默认开放”（fail-open），从而允许 在未经验证的情况下继续执行。 攻击者通过触发 DNS 解析失败或利用 DNS 重绑定攻击，可以绕过 SSRF 防护机制，访问受限的网络资源，包括云元数据端点（例如 169.254.169.254）。

CVSS 5.3 · Medium EPSS 0.34% · P27

Affected Version Matrix 2

VendorProduct Version RangeStatus
nltk nltk < 3.10.0 affected
3.10.0 unaffected
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I. Basic Information for CVE-2026-63311

Vulnerability Information
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Vulnerability Title
NLTK before 3.10.0 SSRF via DNS Resolution Failure
Source: CVE Program / CVE List V5
Vulnerability Description
NLTK before 3.10.0 (affected versions <= 3.9.4) contains a server-side request forgery (SSRF) vulnerability in the validate_network_url() function in nltk/pathsec.py. The _resolve_hostname() helper catches OSError and ValueError during socket.getaddrinfo() and returns an empty list; when DNS resolution fails, the validation loop executes no IP checks and the function fails open, allowing urlopen() to proceed without validation. An attacker who can trigger DNS resolution failures or use DNS rebinding can bypass SSRF protections and reach restricted network resources, including cloud metadata endpoints (e.g., 169.254.169.254).
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
服务端请求伪造(SSRF)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
nltk nltk 0 ~ 3.10.0 -

II. Public POCs for CVE-2026-63311

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III. Intelligence Information for CVE-2026-63311

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Vendor Advisories for CVE-2026-63311 (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-2026-66393 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-2026-63310 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-2026-71514 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-918

V. Comments for CVE-2026-63311

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