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 products
nltk: nltk
References3
- github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55 ExploitVendor Advisory
- www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-… Third Party Advisory
- www.openwall.com/lists/oss-security/2026/09/01/3
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - CVSS 4.0
-
8.7
HIGH
Score source: CNA
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 1% percentile: 51 · as of 9 November 2026
- CWE
- CWE-1333
Could this be exploited in your environment?
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