CVE Catalog
CVE-2026-81725
LowCVSS 3.7Summary
NLTK before 3.10.3 has a regular expression denial of service vulnerability in Pl196xCorpusReader. Attackers can supply malformed TEI blocks causing quadratic CPU consumption.
Risk Assessment
DoS attacks can cause unavailability of services using NLTK, leading to downtime.
Recommendation
Upgrade NLTK to version 3.10.3 or later.
Original NVD description (English source)
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.