CVE-2026-12261Network attack vector

Resource poisoning via missing package ownership checks

Published Aug 7, 2026 · Updated Aug 7, 2026

Improper access control in NLTK 3.9.4 and earlier allows remote attackers to poison installed resources through a malicious data package. The nltk.downloader _unzip_iter path extracts archive members into shared corpora or taggers directories without confirming that each member belongs to the package identifier being installed. Exploitation requires a user to download the malicious package; overwritten resources persist across interpreter restarts and alter later NLTK processing.

CVSS severity5.3
Medium
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in NLTK 3.9.4 and earlier allows remote attackers to poison installed resources through a malicious data package. The nltk.downloader _unzip_iter path extracts archive members into shared corpora or taggers directories without confirming that each member belongs to the package identifier being installed. Exploitation requires a user to download the malicious package; overwritten resources persist across interpreter restarts and alter later NLTK processing.

The record

CVE
CVE-2026-12261
Published
Aug 7, 2026
Updated
Aug 7, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-494, CWE-284, T1195.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 7, 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=unspecified <=latest

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=unspecified <=latest

Published CVSS scores

5.3GCVE DatabaseCVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A: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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-494Download of Code Without Integrity Check
CWE-284Improper Access Control
T1195.001Compromise Software Dependencies and Development Tools

Public exploit references

No public exploit references are available in this record.

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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