Description

NLTK versions before 3.10.0 default to ENFORCE=False in pathsec.py, causing all security validation functions to emit warnings instead of raising exceptions. Attackers can bypass path traversal and pickle deserialization protections by exploiting the disabled security controls that are only active when manually enabled.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-22T15:16:18.967Z",
  "pubdate": "2026-08-22T15:16:18.967Z",
  "executiveSummary": "NLTK versions before 3.10.0 contain a security bypass vulnerability resulting from improper enforcement default configurations within path security validation mechanisms. Specifically, the vulnerability resides in pathsec.py, where the ENFORCE parameter defaults to False. This misconfiguration causes all underlying security validation functions to merely emit warning messages rather than terminating execution by raising exceptions when malicious inputs are encountered. The primary impact of this vulnerability is the complete circumvention of built-in security controls designed to protect against path traversal attacks and arbitrary pickle deserialization flaws. Affected systems include applications utilizing NLTK versions prior to 3.10.0 without manual security enforcement overrides. The risk implications are severe, as unauthorized attackers can bypass intended defensive boundaries. To exploit this vulnerability, an attacker must have the capability to supply malicious input vectors designed to trigger path traversal or insecure deserialization sequences, leveraging the inactive security controls to achieve compromise.",
  "technicalDetails": "The vulnerability stems from flawed defensive design within the pathsec.py component of NLTK. In affected versions prior to 3.10.0, the core security validation logic relies on an internal flag designated as ENFORCE. By default, this flag is initialized to a boolean value of False. Consequently, when security validation functions are invoked to inspect incoming paths or data structures, any anomalous or malicious pattern matching path traversal sequences or dangerous serialization constructs fails to trigger a hard failure. Instead of halting execution and raising an exception, the validation routines log a warning and allow the execution flow to proceed uninterrupted. The vulnerable component is strictly localized to pathsec.py and the associated validation routines that consume the ENFORCE parameter. Attackers exploit this behavior by supplying crafted payloads intended for file operations or deserialization routines. Because the security controls are passively configured, the validation mechanism does not block the payload. In a path traversal scenario, the attacker provides directory traversal sequences that bypass validation, allowing unauthorized file system access. In a pickle deserialization context, the disabled protections permit the processing of untrusted serialized data, potentially leading to arbitrary code execution. The attack flow requires the attacker to interact with application interfaces that process inputs through NLTK functions without manual security hardening. No authentication or elevated privileges are inherently required if the vulnerable functionality is exposed to untrusted input sources. Network exposure depends entirely on how the host application implements NLTK. Post-exploitation impact can range from unauthorized local file disclosure to complete system compromise via insecure deserialization."
}