GHSA-w3v8-gmh9-3wv7: nltk (CVE-2026-80206)

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.

NLTK versions before 3.10.3 are vulnerable to regular expression denial of service through the nltk.tgrep module, which passes user-supplied regular expressions to Python's re engine without a timeout or validation. An attacker who can supply the pattern to tgrep_positions() or tgrep_compile(), such as through a web API, can send a single crafted request that causes catastrophic backtracking and blocks the process indefinitely. Upgrade to NLTK 3.10.3 or later, which contains the fix; alternatively, do not pass untrusted input to tgrep patterns.

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
8.2	High	4.0	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N	CNA (VulnCheck)

CISA KEV Not listed.
EPSS 0.0044, the 38th 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.