CVE-2026-78681

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.

CVSS 4.0

8.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.5% chance of exploitation in the next 30 days; higher than 43% of CVEs (scores of 2026-10-25)

CWE

CWE-776

Published

2026-08-25

Modified

2026-10-12

Record from

the NVD, synced 2026-10-19

Affected

• nltk:nltk

Packages (OSV)

References

• https://github.com/nltk/nltk/security/advisories/GHSA-97qj-x29f-37w7
• https://www.vulncheck.com/advisories/nltk-before-entity-expansion-dos-via-elementtree

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