Executive Summary

A vulnerability in the Natural Language Toolkit (NLTK) library, specifically in versions before 3.10.0, allows attackers to bypass security protections due to an insecure default configuration. This vulnerability, tracked as CVE-2026-62388, has a CVSS score of 7.5 and is considered HIGH severity. The affected component is the pathsec.py module, which controls security validation functions.

Technical Analysis

The vulnerability class is an insecure default configuration. In NLTK versions before 3.10.0, the ENFORCE parameter in pathsec.py defaults to False. This causes all security validation functions to emit warnings instead of raising exceptions, effectively bypassing protections against path traversal and pickle deserialization attacks. The root cause is the missing input validation and improper access control due to the disabled security controls.

How It Gets Exploited

An unauthenticated remote attacker can exploit this vulnerability. The attacker would send a crafted payload to the affected NLTK application, taking advantage of the disabled security controls. For example, an attacker could send a malicious pickle file to a vulnerable NLTK application, which would not properly validate the file due to the insecure default configuration. This could allow the attacker to bypass path traversal and pickle deserialization protections, potentially leading to arbitrary code execution or data exfiltration.

Impact Assessment

The affected products are NLTK versions before 3.10.0. The vulnerability has a CVSS score of 7.5, indicating a HIGH severity level. An attacker could achieve confidentiality impact, potentially leading to data exfiltration. The blast radius is relatively high, as NLTK is a widely-used library in the natural language processing community.

Recommended Actions

To mitigate this vulnerability, users should update NLTK to version 3.10.0 or later. Additionally, users should ensure that security controls are properly enabled and configured in their NLTK applications. Detection guidance: Monitor for suspicious pickle files or unusual network activity that may indicate exploitation attempts.

Sources

  • National Vulnerability Database (NVD)
  • https://nvd.nist.gov/vuln/detail/CVE-2026-62388
  • https://github.com/nltk/nltk/security/advisories/GHSA-p3m8-78j2-g5p3
  • https://www.vulncheck.com/advisories/nltk-before-insecure-default-configuration-pathsec