GHSA-97qj-x29f-37w7: nltk (CVE-2026-78681)

Package	Ecosystem	Affected	Fixed in
nltk	PyPI	<3.10.3	3.10.3

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Versions of NLTK before 3.10.3 are vulnerable to a denial-of-service through entity expansion ("billion laughs") when parsing XML in several places, including load_ace_file, ElementWrapper, and the downloader. An attacker who can supply a crafted XML document of a few hundred bytes can cause megabytes of memory use per parse, and libexpat's built-in cap may not apply. Upgrade to NLTK 3.10.3, which blocks entity declarations in these parsers. No workaround is listed.

Written 5 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
8.7	High	4.0	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0052, the 44th percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:38 UTC First seen by agentprime
31 Oct 2026, 14:38 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.