CVE-2026-81723
Received Received - Intake

NLTK XMLCorpusView Quadratic CPU Exhaustion Vulnerability

Publication date: 2026-08-27

Last updated on: 2026-08-27

Assigner: VulnCheck

Description
NLTK versions before 3.10.3 contain a quadratic CPU exhaustion vulnerability in XMLCorpusView._read_xml_fragment() that rescans accumulated XML fragments on every 1 KiB block read. Attackers can provide malformed XML corpus files to cause severe CPU consumption and denial of service through affected readers like BNCCorpusReader.

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Meta Information

Published
2026-08-27
Last Modified
2026-08-27
Generated
2026-08-27
AI Q&A
2026-08-27
EPSS Evaluated
N/A
NVD
CVE-2026-81723
EUVD
EUVD-2026-67073

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
nltk nltk to 3.10.3 (exc)

Helpful Resources

Exploitability

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

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Executive Summary

CVE-2026-81723 is a quadratic CPU exhaustion vulnerability in NLTK versions before 3.10.3. The XMLCorpusView._read_xml_fragment() function inefficiently processes malformed XML files by repeatedly rescanning accumulated 1 KiB blocks against a regular expression. This causes computational work to grow quadratically with input size, leading to excessive CPU usage and potential denial of service.

Detection Guidance

Check NLTK version with pip show nltk. If version is below 3.10.3, the system is vulnerable. Monitor CPU usage spikes when processing XML corpus files. Look for malformed XML files in NLTK corpus directories.

Impact Analysis

This vulnerability can cause severe CPU consumption and system slowdowns when processing malformed XML files. It may lead to denial of service, making systems unresponsive or crashing. Users relying on affected NLTK corpus readers like BNCCorpusReader could experience degraded performance or service interruptions.

Mitigation Strategies

Upgrade NLTK to version 3.10.3 or later using pip install --upgrade nltk. Remove or sanitize any untrusted XML corpus files in NLTK directories. Disable affected corpus readers like BNCCorpusReader if not needed.

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