CVE-2026-109956 NLTK through 3.10.3 Path Traversal via WekaClassifier Model Path
Attackers can bypass path restrictions in NLTK's WekaClassifier to read or write files outside allowed directories via unvalidated model paths.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-109956?
CVE-2026-109956 is a high-severity path traversal vulnerability in nltk, published on 13 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
NLTK through 3.10.3 contains a path traversal vulnerability in WekaClassifier that allows attackers to bypass nltk.pathsec containment by supplying unvalidated model paths. Attackers controlling the model_filename or model argument can make the weka JVM write files via -d or probe files via -l outside allowed data roots.
Weakness: CWE-22
Which versions are affected by CVE-2026-109956?
2 open source packages ship an affected version, including nltk.
| Package | Affected | Fixed in |
|---|---|---|
nltk PyPI | All versions | 3.10.4 |
nltk PyPI | All versions | 3.10.4 |
How do I fix CVE-2026-109956?
Upgrade nltk to 3.10.4 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-109956 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-109956 exists.
Sources
Also known as DEBIAN-CVE-2026-109956, ECHO-d53c-5278-1d0e, GHSA-9fgx-q9j8-3j83, GHSA-j456-xh4h-cpf2, UBUNTU-CVE-2026-109956.