CVE-2026-12252 in nltk
Summary
by MITRE • 07/04/2026
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.
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Analysis
by VulDB Data Team • 07/07/2026
The vulnerability in nltk/nltk versions 3.9.3 and earlier represents a critical security flaw affecting five Stanford interface classes that enable integration with Stanford NLP tools through Java-based JAR executables. These classes including StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser all share a common design pattern that accepts user-controllable JAR file paths and executes them through the java() function which internally leverages subprocess.Popen() without any integrity verification mechanisms. This architectural weakness creates an arbitrary code execution vector where malicious actors can load and execute untrusted JAR files with elevated privileges, effectively bypassing security boundaries that should normally prevent such operations.
The technical implementation of this vulnerability stems from insufficient input validation and trust verification within the Stanford interface classes. When users provide JAR file paths to these components, the system does not perform cryptographic verification or integrity checks before executing the specified Java archives. The java() function acts as a direct conduit to subprocess.Popen(), which executes the Java command with the provided JAR path without any sanitization or verification steps that would normally be required for security-sensitive operations. This design pattern violates fundamental security principles and creates an attack surface where an attacker could substitute a legitimate JAR file with a malicious one containing unauthorized code execution capabilities.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass full system compromise potential, particularly in environments where NLTK applications process untrusted user input or operate with elevated permissions. An attacker could exploit this weakness by crafting a malicious JAR file that executes arbitrary commands when loaded by any of the affected Stanford interface classes, potentially leading to data exfiltration, system persistence mechanisms, or lateral movement within networked environments. The vulnerability affects all versions up to and including 3.9.3, making it a widespread concern for organizations relying on NLTK for natural language processing tasks that might involve external data sources or user-provided content.
This vulnerability maps directly to CWE-494 in the Common Weakness Enumeration catalog, which specifically addresses "Download of Code Without Integrity Check" and falls under the broader category of code injection vulnerabilities. The ATT&CK framework categorizes this issue within the privilege escalation and execution phases, specifically mapping to techniques such as T1059.007 for command and scripting interpreter and T1203 for Exploitation for Client Execution. The lack of SHA256 verification that was implemented for StanfordSegmenter in CVE-2026-0848 demonstrates a pattern of incomplete security remediation where similar vulnerabilities were not consistently addressed across related components, leaving organizations with a false sense of security despite partial fixes being applied to some but not all affected classes. The recommended mitigation strategy involves implementing cryptographic verification mechanisms identical to those used for StanfordSegmenter, including SHA256 hash validation of JAR files before execution, and ensuring that all user-controllable JAR paths undergo strict integrity verification processes before any Java subprocess execution occurs.