Vulnerability · Published Aug 26, 2026 · Assigned by VulnCheck

CVE-2026-80205NLTK before 3.10.0 ReDoS via Text.findall() unvalidated regex

High 7.5

In plain English

A high-severity regular-expression denial of service in nltk from nltk. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 51% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.7%top 48.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

NLTK versions before 3.10.0 contain a regular expression denial of service vulnerability in Text.findall() and TokenSearcher.findall() methods that accept user-supplied regular expressions without validation or timeout. Attackers can supply crafted regex patterns that cause catastrophic backtracking, resulting in indefinite CPU saturation and denial of service to all users of the Python process.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nltk	no fix listed	DEBIAN-CVE-2026-80205
Debian:13	nltk	no fix listed	DEBIAN-CVE-2026-80205
Debian:14	nltk	3.10.0-1	DEBIAN-CVE-2026-80205
PyPI	nltk	3.10.0	GHSA-rrv8-h7p8-rx55
PyPI	nltk	3.10.0	PYSEC-2026-3750

Affected products (as reported)

Vendor	Product	Versions
nltk	nltk	0 – before 3.10.0

Weakness: CWE-1333 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

GitHub Security Advisory (GHSA-rrv8-h7p8-rx55) vendor-advisory
VulnCheck Advisory: NLTK before 3.10.0 ReDoS via Text.findall() unvalidated regex third-party-advisory
http://www.openwall.com/lists/oss-security/2026/09/01/3