TI-2026-56371 Aliases CVE-2026-81723 GHSA-vp2x-qp44-57v7

NLTK before 3.10.3 Quadratic CPU Exhaustion via XMLCorpusView

MEDIUM 61CWE-400Published 2026-08-27 · Updated 2026-08-31

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: High
Attack requirements: Present
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · Low
Fix status: Partial Red Hat: 5 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-400.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.00281 20th percentileScored 2026-11-07

Fix Partial nltk (nltk): 3.10.3nltk (PyPI): 3.10.3Red Hat: 5 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: Poc
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
nltk	nltk	before 3.10.3	3.10.3	Patch available	CNA
—	nltk (PyPI)	before 3.10.3	3.10.3	Patch available	GHSA-vp2x-qp44-57v7

nltk Vendornltk Affected before 3.10.3 Fixed in 3.10.3 Patch available CNA
nltk (PyPI) Vendor— Affected before 3.10.3 Fixed in 3.10.3 Patch available GHSA-vp2x-qp44-57v7

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPE	Versions	Role	Vendor
cpe:2.3:a:nltk:nltk::::::::	—	—	nltk

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* Versions — — ·nltk

Remediation

Fix · CNA nltk (nltk) Fixed in 3.10.3
Fix · GHSA-vp2x-qp44-57v7 nltk (PyPI) Fixed in 3.10.3 Advisory →

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

Release · 2026-08-27
nltk 3.10.3
5 records Highest priority Priority HIGH 2 HIGH, 2 MEDIUM, 1 LOW
Other records, highest priority first
- TI-2026-56370 nltk PorterStemmer before 3.10.3 Quadratic-time DoSPriority HIGH 77
- TI-2026-56372 NLTK before 3.10.3 Denial of Service via Uncontrolled RecursionPriority HIGH 70
- TI-2026-56375 NLTK before 3.10.3 Hardlink File Overwrite via downloaderPriority MEDIUM 64
Show all 5 records →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
Exploit Intelligence	Affected	No fix planned: Out of support scope
Lightspeed Core	Affected	No fix yet: Fix deferred
OpenShift Lightspeed	Affected	No fix yet: Fix deferred
Red Hat Ansible Automation Platform 2	Affected	No fix planned: Out of support scope
Red Hat OpenShift AI (RHOAI)	Affected	No fix yet: Fix deferred

Timeline

2026-10-02 Threatist record created from CVE-2026-81723
2026-10-03 Alias added: GHSA-vp2x-qp44-57v7

References

Advisory 2

Other 3

TI-2026-00629 Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading CVSS 3.0CRITICAL 10.0
TI-2025-12800 Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution CVSS 3.0CRITICAL 10.0
TI-2026-55173 NLTK before 3.10.3 JVM Argument Injection via Per-Call Options CVSS 4.0CRITICAL 9.3
TI-2026-55155 NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization CVSS 4.0CRITICAL 9.3
TI-2026-56370 nltk PorterStemmer before 3.10.3 Quadratic-time DoS CVSS 4.0HIGH 8.7
TI-2026-55172 NLTK 3.10.2 Path Traversal via corpus-reader constructors CVSS 4.0HIGH 8.8

See all 46 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences