High severity · published Aug 26, 2026
CVE-2026-80205
NLTK before 3.10.0 ReDoS via Text.findall() unvalidated regex
7.5
CVSS
0.7%
EPSS
No
On KEV
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.
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)0.7% · higher than 51% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
NL
nltk · nltk
before 3.10.0 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-80205
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-80205
Exploit
https://github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55
Third Party Advisory
https://www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-findall-unvalidated-regex
www.openwall.com
http://www.openwall.com/lists/oss-security/2026/09/01/3
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