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VulnerabilityPublished

CVE-2026-12259: nltk/nltk · Download of Code Without Integrity Check

Affects nltk/nltkSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium.

Data as of 1 Nov 2026, 22:58 UTC

CVSS 3.0 base score
5.3Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.1% chance of exploitation in 30 days – higher than 0% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 3 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 1 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
nltknltk/nltkAffected
  • ≥ unspecified, ≤ latest
Fixed in–

AI-suggested

Until an official fix is available, users should avoid downloading packages from untrusted sources or mirrors and consider verifying package integrity manually if possible.

Description

CVE-2026-12259 is a medium severity vulnerability in nltk version 3.9.4 where the downloader component may write and extract package data before verifying integrity checks such as SHA-256 or MD5. This flaw allows an attacker who can manipulate the package source (e.g., via a compromised mirror or malicious proxy) to substitute malicious package content. As a result, downstream users or applications may trust and use attacker-controlled corpus or model data.

References

Community reviews

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