Resource exhaustion in Nltk
CVE-2026-81725
NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.
Vulnerability class: DoS (Denial of Service)
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L.
Affected products
Weakness classification (CWE)
References
- disclosure@vulncheck.com (vendor-advisory)
- disclosure@vulncheck.com (third-party-advisory)
Frequently asked questions
- What is CVE-2026-81725?
- CVE-2026-81725 is a low-severity vulnerability in Nltk, classified under Uncontrolled Resource Consumption. CVSS score: 3.7/10. Published 2026-08-27.
- How severe is CVE-2026-81725?
- Low severity. CVSS v3 base score is 3.7 out of 10.