Vulnerability in Nltk
CVE-2026-80205
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.
Vulnerability class: ReDoS (Regular Expression Denial of Service)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.007 (49.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 50th percentile — 49.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.005 · newest: 0.007 · change: +0.002
Affected products
Weakness classification (CWE)
References
- github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55 (Exploit, vendor-advisory, Vendor Advisory)
- www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-findall-unvalida… (Third Party Advisory, third-party-advisory)
- af854a3a-2127-422b-91ae-364da2661108
Frequently asked questions
- What is CVE-2026-80205?
- CVE-2026-80205 is a high-severity vulnerability in Nltk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2026-08-26.
- How severe is CVE-2026-80205?
- High severity. CVSS v3 base score is 7.5 out of 10.