CVE-2026-81724
Description
A flaw was found in NLTK. This uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader allows unauthenticated attackers to cause a denial of service. Attackers can achieve this by supplying deeply nested feature-structure input, which can lead to applications crashing when parsing user-supplied feature structures or feature grammars.
Statement
This flaw in NLTK's nltk.featstruct.FeatStructReader allows unauthenticated attackers to cause a denial of service. By providing deeply nested feature-structure input, applications processing untrusted data can experience crashes due to uncontrolled recursion, impacting service availability.
Mitigation
Applications that process untrusted feature-structure input using NLTK should implement robust input validation and sanitization to prevent deeply nested structures from being processed by `nltk.featstruct.FeatStructReader`. If input cannot be validated, avoid processing untrusted feature-structure input with affected versions of NLTK.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7.5 | N/A | 5.3 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | None | N/A | None |
| User Interaction | None | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | Low |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Frequently Asked Questions
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