Uncontrolled Recursion in Natural Language Toolkit - CVE-2026-81724
Published: August 15, 2026 / Updated: September 14, 2026
Vulnerability identifier: #VU142774
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-81724
CWE-ID: CWE-674
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 uncontrolled recursion in nltk.featstruct.FeatStructReader when parsing deeply nested feature-structure or feature-grammar input. A remote attacker can send a specially crafted nested input to cause a denial of service.
The issue is reachable through both FeatStruct(str) and FeatureGrammar.fromstring() when applications parse externally supplied text.
Affected software
Natural Language Toolkit
How to mitigate CVE-2026-81724
Install security update from vendor's website.
Natural Language Toolkit - update to 3.10.3