CVE-2026-63310Public exploitNetwork attack vector

Malicious package injection via unchecked downloads

Published Aug 22, 2026 · Updated Aug 22, 2026

Package injection in the NLTK downloader before 3.9.3 allows remote attackers to install malicious data through intercepted downloads. The downloader moves the received archive to its final path and calls _unzip_iter() without comparing its SHA-256 digest to the package index. Exploitation requires a victim-initiated package download plus control of traffic, DNS resolution, or a shared-filesystem race, and permits attacker-chosen package contents to be installed.

CVSS severity9.3
Critical
EPSS probabilityUnavailable
No score available in this record
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

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Summary

What happened

Package injection in the NLTK downloader before 3.9.3 allows remote attackers to install malicious data through intercepted downloads. The downloader moves the received archive to its final path and calls _unzip_iter() without comparing its SHA-256 digest to the package index. Exploitation requires a victim-initiated package download plus control of traffic, DNS resolution, or a shared-filesystem race, and permits attacker-chosen package contents to be installed.

The record

CVE
CVE-2026-63310
Published
Aug 22, 2026
Updated
Aug 22, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-494, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 22, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.9.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=0 <3.9.3

Published CVSS scores

7.1VulnCheckCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:H/A:H
9.3VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-494Download of Code Without Integrity Check
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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