CVE-2026-12259: nltk/nltk · Download of Code Without Integrity Check
Affects nltk/nltkSource CVE Database V5
Not known to be exploited · CVSS 5.3 Medium.
Data as of 1 Nov 2026, 22:58 UTC
- 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:NExploitation evidence
Disclosed: evidence found.
CVE published 3 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| nltknltk/nltk | Affected
| 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.