High severity · published Aug 25, 2026
CVE-2026-78681
NLTK before 3.10.3 Entity Expansion DoS via ElementTree
7.5
CVSS
0.5%
EPSS
No
On KEV
Description
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 vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 44% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NL
nltk · nltk
before 3.10.3 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-78681
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-78681
Exploit
https://github.com/nltk/nltk/security/advisories/GHSA-97qj-x29f-37w7
Third Party Advisory
https://www.vulncheck.com/advisories/nltk-before-entity-expansion-dos-via-elementtree
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