← Vulnerability feed

Vulnerability record · CVE-2026-80205 · published 26 August 2026

CVE-2026-80205: Nltk inefficient regular expression (redos) vulnerability

Nltk · Nltk

NLTK versions before 3.10.0 contain a regular expression denial of service vulnerability in Text.findall() and TokenSearcher.findall() methods that accept user-supplied regular expressions without validation or timeout. Attackers can supply crafted regex patterns that cause catastrophic backtracking, resulting in indefinite CPU saturation and denial of service to all users of the Python process.

8.7 CVSS 4.0 High EPSS 0.65% · top 50.9% CWE-1333 · Inefficient regular expression (ReDoS)
8.7CVSS 4.0 base score
0.65%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References, 1 tagged exploit
3 Sep 2026Last modified by NVD

Description

NLTK versions before 3.10.0 contain a regular expression denial of service vulnerability in Text.findall() and TokenSearcher.findall() methods that accept user-supplied regular expressions without validation or timeout. Attackers can supply crafted regex patterns that cause catastrophic backtracking, resulting in indefinite CPU saturation and denial of service to all users of the Python process.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55 ExploitVendor Advisory
https://www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-findall-unvalidated-regex Third Party Advisory
http://www.openwall.com/lists/oss-security/2026/09/01/3

Track CVE-2026-80205 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2026-0848Nltk improper input validation vulnerabilityNLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the StanfordSegmenter module. The module dynamic…EPSS 0.81%9.4CVE-2026-78683Nltk deserialization of untrusted data vulnerabilityNLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/p…EPSS 0.51%9.3CVE-2026-79675Nltk argument injection vulnerabilityNLTK before 3.10.3 fails to validate JVM options passed through the per-call options parameter in the java() function, allowing attackers to inject d…EPSS 0.78%9.3CVE-2026-79657Nltk deserialization of untrusted data vulnerabilityNLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire module namespaces instead o…EPSS 1.3%8.8CVE-2026-79674Nltk vulnerabilityNLTK versions before 3.10.3 contain a path sandbox bypass vulnerability in corpus-reader constructors that allows attackers to read files outside the…EPSS 0.39%8.8CVE-2025-14009Nltk code injection vulnerabilityA critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter function in nltk/downloader.py…EPSS 0.95%8.7CVE-2026-81722Nltk vulnerabilitynltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). …EPSS 0.52%8.7CVE-2026-78681Nltk vulnerabilityNLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers …EPSS 0.52%

Source: NIST National Vulnerability Database (record CVE-2026-80205), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.