SB2026080754 - Multiple vulnerabilities in Natural Language Toolkit

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Main Vulnerability Database SB2026080754

SB2026080754 - Multiple vulnerabilities in Natural Language Toolkit

Published: August 7, 2026 Updated: September 14, 2026

Security Bulletin ID SB2026080754
CSH Severity
High
Patch available
YES
Number of vulnerabilities 3
Exploitation vector Remote access
Highest impact Data manipulation

Breakdown by Severity

High 33% Medium 67%
  • Low
  • Medium
  • High
  • Critical

Description

This security bulletin contains information about 3 vulnerabilities.


1) Download of code without integrity check (CVE-ID: CVE-2026-63310)

CWE-ID: CWE-494 - Download of Code Without Integrity Check

CVSSv4: 8.8 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to inject malicious packages.

The vulnerability exists due to download of code without integrity check in the package downloader in nltk/downloader.py when downloading and extracting packages. A remote attacker can tamper with a downloaded package or supply a crafted package archive to inject malicious packages.

Exploitation may be possible via a man-in-the-middle attack during HTTP downloads, DNS poisoning to redirect requests to an attacker-controlled server, or a race condition on shared filesystems between file replacement and extraction.


2) Uncontrolled Recursion (CVE-ID: CVE-2026-12876)

CWE-ID: CWE-674 - Uncontrolled Recursion

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to uncontrolled recursion in RecursiveDescentParser and SteppingRecursiveDescentParser when parsing crafted ambiguous or left-recursive grammars. A remote attacker can provide a crafted grammar or input to cause a denial of service.

The issue can result in unbounded CPU consumption or exhaustion of the Python recursion stack, affecting availability of a single process.


3) Inefficient Algorithmic Complexity (CVE-ID: CVE-2026-81722)

CWE-ID: CWE-407 - Inefficient Algorithmic Complexity

CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]


The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to inefficient algorithmic complexity in nltk.stem.PorterStemmer.stem() when processing a token containing a long run of the letter 'y' followed by a suffix such as 'ness'. A remote attacker can submit a specially crafted token to cause a denial of service.

The issue affects single-process availability only and does not impact confidentiality or integrity.


Remediation

Install update from vendor's website.

References