CVE-2026-12261: nltk/nltk · Improper Access Control
Affects nltk/nltkSource CVE Database V5
Not known to be exploited · CVSS 5.3 Medium.
Data as of 5 Nov 2026, 00:01 UTC
- EPSS
- 0.2% chance of exploitation in 30 days – higher than 11% 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 7 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 5 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| nltknltk/nltk | Affected
| Fixed in– |
AI-suggested
Until a fix is available, users should avoid installing untrusted or unverified packages via nltk.downloader and consider isolating environments to prevent cross-package contamination. Monitor official nltk channels for updates addressing this vulnerability.
Description
CVE-2026-12261 is a medium severity vulnerability in the nltk Python library's downloader component (nltk.downloader) affecting versions up to 3.9.4. The flaw allows cross-package resource and model poisoning because the downloader extracts package archives into shared namespaces without proper isolation and only validates package integrity after extraction. This enables one package to overwrite another's trusted resources, which remain active across interpreter restarts and can impact workflows relying on NLTK APIs.