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NLTK EUVDEUVD-2026-64335

| CVE-2026-63310 CRITICAL
Download of Code Without Integrity Check (CWE-494)
2026-08-22 VulnCheck GHSA-gf32-cmjh-8m9v
Code Injection Nltk
9.3
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/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
vuln.today AI
7.5 HIGH

AC:H and UI:R because exploitation needs an attacker-held MITM/DNS position plus a victim-initiated download; PR:N as no NLTK auth is required; full C/I/A impact from injected content.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Analysis Generated
Aug 22, 2026 - 15:03 vuln.today
Patch available
Aug 22, 2026 - 15:01 EUVD
CVE Published
Aug 22, 2026 - 14:12 cve.org
CRITICAL 9.3

DescriptionCVE.org

NLTK before 3.9.3 fails to verify file integrity after downloading packages and before extraction in the downloader module. Attackers can perform man-in-the-middle attacks or DNS poisoning to inject malicious package contents that are extracted without validation.

AnalysisAI

Arbitrary code injection in the Natural Language Toolkit (NLTK) before 3.9.3 stems from the downloader module extracting downloaded corpora and model packages without verifying their integrity, allowing an attacker positioned to tamper with the download (man-in-the-middle or DNS poisoning) to substitute malicious archive contents that are unpacked onto the victim host. All NLTK versions prior to 3.9.3 are affected (CWE-494). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Gain MITM or DNS-poisoning position on victim network
Delivery
Victim triggers NLTK package download
Exploit
Spoof response with malicious archive
Execution
NLTK extracts contents without integrity check
Persist
Poisoned files loaded/executed
Impact
Code injection or data corruption
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Vulnerability AssessmentAI

Exploitation Exploitation requires the victim to actively trigger a package download via NLTK's downloader module (nltk.download / nltk.downloader) on a version below 3.9.3, AND the attacker to occupy a privileged network position to alter that download - specifically a man-in-the-middle vantage or the ability to poison DNS resolution for the download endpoint. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 base score is 9.3 (Critical) with vector AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H, which on its face implies trivial unauthenticated network exploitation with full impact. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A developer or CI pipeline running NLTK < 3.9.3 invokes nltk.download() while on a network an attacker can influence; the attacker uses ARP/DNS spoofing to answer the package request with a malicious archive. NLTK extracts the tampered contents without validation, planting attacker-controlled files (e.g., a poisoned pickled model) that execute or corrupt data when subsequently loaded. …
Remediation Upgrade to NLTK 3.9.3 or later, which adds post-download integrity verification (Vendor-released patch: 3.9.3); pin this minimum version in requirements files and lockfiles across all environments, including CI and container images. … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, identify all applications and systems running NLTK versions prior to 3.9.3 and assess internet connectivity and update mechanisms. …

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EUVD-2026-64335 vulnerability details – vuln.today
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