CVE-2026-12252 Untrusted JAR Code Execution in Multiple Stanford Interface Classes in nltk/nltk
Attackers can execute arbitrary code by providing malicious JAR files to Stanford interface classes in the NLTK library due to missing integrity checks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-12252?
CVE-2026-12252 is a high-severity code injection vulnerability in nltk/nltk, published on 4 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser) are vulnerable to untrusted JAR code execution. These classes accept user-controllable JAR paths and execute them via the `java()` function, which invokes `subprocess.Popen()` without integrity verification. This vulnerability is identical to CVE-2026-0848, which was fixed for StanfordSegmenter by adding SHA256 verification. However, the fix was not applied to these additional classes, leaving them susceptible to arbitrary code execution when loading untrusted JAR files.
Weakness: CWE-94
Which versions are affected by CVE-2026-12252?
3 open source packages ship an affected version, including nltk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nltk PyPI | All versions | 3.9.4 |
nltk PyPI | All versions | 3.9.4 |
nltk PyPI | All versions | 3.9.4 |
Products include Nltk Nltk.
How do I fix CVE-2026-12252?
Upgrade nltk to 3.9.4 or later.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-12252 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12252 exists.
Other vulnerabilities in nltk/nltk
- CVE-2026-0848 Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading
- CVE-2025-14009 Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution
- CVE-2026-78683 NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
- CVE-2026-79657 NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization
- CVE-2026-79675 NLTK before 3.10.3 JVM Argument Injection via Per-Call Options
Sources
Also known as DEBIAN-CVE-2026-12252, ECHO-aca5-37c5-5309, GHSA-9r6g-266r-89x4, MINI-j5j2-v7mg-2rqv, PYSEC-2026-2085, UBUNTU-CVE-2026-12252.