EUVD-2026-65228
GHSA-crp9-r7rq-c8cg
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
AC:H reflects the non-default proxy requirement; S:C because the proxy fetches internal resources outside the application's trust boundary; I:L for attacker-influenced package installation.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
3DescriptionCVE.org
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.
AnalysisAI
Server-side request forgery in NLTK before 3.10.3 allows unauthenticated remote attackers to reach internal HTTP services and load attacker-controlled downloader indexes when an HTTP proxy is configured. The flaw sits in nltk.pathsec.urlopen and its callers (nltk.data.load, nltk.downloader.Downloader.index, nltk.downloader.Downloader.download): local hostname validation passes the supplied public URL, but proxy-handler inheritance then replaces NLTK's safe URL handlers so the actual fetch is executed by the proxy against an internally-resolvable destination that is never re-validated. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that an HTTP proxy be configured in the environment running NLTK - typically via the HTTP_PROXY or HTTPS_PROXY environment variables or equivalent urllib proxy settings. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N) places this at a high base score, but several factors modulate real-world priority. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker targeting a data-science API that accepts a user-supplied corpus URL and passes it to nltk.data.load constructs a URL pointing to a legitimate public hostname. Because the deployment runs behind a corporate HTTP proxy, the proxy resolves the supplied hostname to an internal metadata service (e.g., 169.254.169.254 on a cloud instance); NLTK's local validation cleared the public hostname and never re-checks the proxy's resolved destination. … |
| Remediation | Upgrade NLTK to version 3.10.3 or later, which resolves the proxy-handler inheritance flaw in pathsec.urlopen. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, conduct inventory of all systems running NLTK versions before 3.10.3 and audit which deployments have HTTP proxy configurations enabled. …
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Same weakness CWE-918 – Server-Side Request Forgery (SSRF)
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External POC / Exploit Code
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