CVE-2026-78681: Nltk

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

NLTK versions before 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes to megabytes in memory, causing denial of service.

Affected products

• Nltk Nltk: before 3.10.3 (fixed in 3.10.3)

Published 2026-08-25. Last modified 2026-09-01.