Description

NLTK before 3.10.0 contains an arbitrary local file read vulnerability in StreamBackedCorpusView that bypasses pathsec.ENFORCE by calling builtins.open() directly instead of pathsec.open(). Attackers who control the fileid argument can read arbitrary local files regardless of the ENFORCE setting, including sensitive system files and application credentials.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.5",
  "pubDate": "2026-08-22T15:16:19.367Z",
  "pubdate": "2026-08-22T15:16:19.367Z",
  "executiveSummary": "NLTK before 3.10.0 is vulnerable to an arbitrary local file read vulnerability, categorized as an improper access control and path traversal issue.\nThe vulnerability allows malicious actors to read sensitive system files and application credentials by exploiting insecure file handling mechanisms.\nThe affected product is NLTK, specifically versions prior to 3.10.0, impacting applications that utilize corpus reading functionalities.\nThe risk implications are severe, as unauthorized data exposure can lead to complete system compromise or leakage of confidential information.\nAttackers require control over the fileid argument within the affected component to successfully execute the attack.\nNo complex authentication or network exposure is explicitly required if the application processes untrusted inputs passed directly to the vulnerable function.",
  "technicalDetails": "The root cause of the vulnerability lies within the StreamBackedCorpusView component of NLTK, which fails to properly enforce security constraints defined by pathsec.ENFORCE.\nSpecifically, the vulnerable component bypasses pathsec.ENFORCE by directly calling the built-in open() function instead of utilizing pathsec.open().\nBecause pathsec checks are circumvented, input validation and path restriction mechanisms are rendered ineffective against malicious file paths supplied via the fileid parameter.\nThe exploitation method relies on supplying a crafted path or directory traversal sequence within the fileid argument controlled by the attacker.\nThe attack flow proceeds as follows: an attacker identifies an application input vector that passes data into the fileid argument of StreamBackedCorpusView; the attacker supplies an arbitrary file path targeting sensitive local resources, such as system configuration files or application credentials; the component processes the input and initiates a direct call to builtins.open(); the operating system honors the file access request due to lacking application-level restrictions; and the contents of the target file are returned or processed by the application, exposing sensitive data to the attacker.\nThe affected component is StreamBackedCorpusView, and the vulnerability impacts all NLTK versions prior to 3.10.0.\nThe vulnerability operates locally or via application interfaces that expose the corpus view parameters to external users, bypassing standard defensive path security boundaries."
}