What’s Vulnerable › Vulnerabilities

CVE-2026-80205: NLTK before 3.10.0 ReDoS via Text.findall() unvalidated regex

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-08-26 · updated 2026-09-03
• Weakness: CWE-1333

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.

Affected products

• nltk: before 3.10.0 — fixed in 3.10.0

How to fix

Upgrade to a fixed version: nltk 3.10.0. Check the vendor advisory for mitigations.

References

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

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