Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

Critical severity, with a CVSS score of 9.8, published 25 August 2026.

Is there a fix for This vulnerability?

A patch was published on 2026-08-11: Version 3.10.3 patched Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

Check whether you run nltk (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

NLTK JVM argument injection in Stanford wrappers via per-call options

Severity: critical · CVSS 9.8 · Published 2026-08-25

NLTK is a popular Python library used for natural language processing tasks that includes wrappers for Stanford NLP tools. A validation bypass allows attackers to inject malicious Java arguments through wrapper class options, leading to arbitrary code execution on systems running NLTK-based services. This bypasses a prior security fix and could compromise applications that accept user-supplied configuration for NLP processing.

Technologies: nltk (PyPI). Vendors: PyPI.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: Critical severity, with a CVSS score of 9.8, published 25 August 2026.
Which products and versions are affected?: nltk (PyPI) <= 3.10.2.
Is there a fix for This vulnerability?: A patch was published on 2026-08-11: Version 3.10.3 patched Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: Check whether you run nltk (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is an argument injection flaw (CWE-88) in NLTK's java() function. While a previous CVE-2026-12841 fix added _validate_java_options() to block dangerous JVM flags (like -agentpath, -javaagent, @argfile) when using config_java(), the validation was not applied to per-call options passed directly to java(). The four Stanford wrapper classes (GenericStanfordParser, StanfordTagger, StanfordTokenizer, StanfordSegmenter) accept user-supplied java_options and route them through the unvalidated per-call path, bypassing the fix entirely. An attacker can inject flags like -agentpath:/path/to/malicious.so or -javaagent:/path/to/malicious.jar to load arbitrary code within the JVM. The fix is to add _validate_java_options() call in the java() function's per-call options handling. Patched in NLTK 3.10.3.

Affected products

NLTK Project NLTK < 3.10.3

Timeline

2026-08-25: disclosed
2026-08-11: patched: Version 3.10.3 patched

References

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