Inefficient Algorithmic Complexity in Natural Language Toolkit - CVE-2026-81722
Published: August 15, 2026 / Updated: September 14, 2026
Vulnerability identifier: #VU142777
CSH Severity: Medium
CVSS v4: 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]
CVE-ID: CVE-2026-81722
CWE-ID: CWE-407
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
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.
Affected software
Natural Language Toolkit
How to mitigate CVE-2026-81722
Install security update from vendor's website.
Natural Language Toolkit - update to 3.9.3