CVE-2026-12252 affects nltk/nltk versions up to 3.9.3 in five Stanford interface classes: StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser. These classes accept user-controlled JAR file paths and execute them using the java() function, which internally calls subprocess.Popen() without verifying the integrity of the JAR files. This lack of verification enables an attacker to execute arbitrary code by supplying malicious JAR files. The vulnerability is identical in nature to CVE-2026-0848, which was fixed for the StanfordSegmenter class by adding SHA256 verification of JAR files. However, the fix was not extended to these other classes, leaving them vulnerable.

Successful exploitation can lead to arbitrary code execution on the host system with the privileges of the user running the nltk process. This can compromise confidentiality, integrity, and availability of the affected system. The CVSS score of 7.8 (high) reflects the significant impact and the low attack complexity, although user interaction is required.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until an official fix is released, users should avoid loading untrusted JAR files with the affected Stanford interface classes. Applying the SHA256 verification approach used in CVE-2026-0848 to these classes is recommended once a patch is available.