TI-2026-55447 Aliases CVE-2026-80206 GHSA-w3v8-gmh9-3wv7

NLTK 3.10.2 Regular Expression Denial of Service via tgrep

HIGH 69CWE-1333Published 2026-08-26 · Updated 2026-08-26

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 · High
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-1333.

Summary

NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV

EPSS 0.0044 38th percentileScored 2026-11-07

Public exploit Yes 1 exploit referenceTagged by NVD

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-w3v8-gmh9-3wv7

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-w3v8-gmh9-3wv7

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:nltk:nltk::::::::	before 3.10.3	Vulnerable	nltk

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* Versions before 3.10.3 Vulnerable ·nltk

Remediation

Fix · CNA nltk (nltk) Fixed in 3.10.3
Fix · GHSA-w3v8-gmh9-3wv7 nltk (PyPI) Fixed in 3.10.3 Advisory →

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-2026-80206
2026-10-03 Alias added: GHSA-w3v8-gmh9-3wv7

References

Exploit 1

GitHub Security Advisory (GHSA-w3v8-gmh9-3wv7)

Advisory 1

https://nvd.nist.gov/vuln/detail/CVE-2026-80206

Other 4

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 41 →

Sources

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