CVE-2026-126303
Awaiting Analysis Awaiting Analysis - Queue

Uncontrolled Resource Consumption in NLTK via Ambiguous Grammar

Publication date: 2026-11-13

Last updated on: 2026-11-13

Assigner: VulnCheck

Description
NLTK before 3.10.4 contains an uncontrolled resource consumption vulnerability in SteppingRecursiveDescentParser.parse() that lacks any max_time deadline or step limit. Attackers influencing the grammar can supply an ambiguous self-embedding grammar and short token input to force unbounded top-down search, pinning CPU cores and exhausting worker pools.

CVSS Scores

EPSS Scores

Probability:
Percentile:

Meta Information

Published
2026-11-13
Last Modified
2026-11-13
Generated
2026-11-13
AI Q&A
2026-11-13
EPSS Evaluated
N/A
NVD
CVE-2026-126303
EUVD
EUVD-2026-125218

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
nltk nltk to 3.10.4 (exc)

Helpful Resources

Exploitability

CWE
CWE Icon
KEV
KEV Icon
CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

AI Quick Actions

Instant insights powered by AI
Executive Summary

This vulnerability is an uncontrolled resource consumption issue in NLTK versions before 3.10.4. The SteppingRecursiveDescentParser.parse() function lacks a max_time deadline or step limit, allowing attackers to exploit ambiguous grammars with short inputs to force unbounded top-down search. This can pin CPU cores and exhaust worker pools.

Detection Guidance

Detecting this vulnerability requires checking the NLTK version in use. Run 'pip show nltk' or 'python -c "import nltk; print(nltk.__version__)"' to verify if the installed version is below 3.10.4. If so, the system is vulnerable.

Impact Analysis

This vulnerability can lead to denial-of-service conditions by consuming excessive CPU resources. Systems using NLTK for natural language processing may experience performance degradation, crashes, or become unresponsive due to unbounded parsing operations.

Mitigation Strategies

Upgrade NLTK to version 3.10.4 or later immediately using 'pip install --upgrade nltk'. If upgrading is not possible, restrict untrusted input processing or implement custom grammar validation to prevent ambiguous self-embedding grammars.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-126303. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart

Security Radar

News mentioning this vulnerability
Loading related security news...