CVE-2026-81725
NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader
MEDIUM 6.3EPSS 0.4%
NLTK before 3.10.3 contains a regular expression denial of service vulnerability in Pl196xCorpusReader that allows attackers to cause quadratic CPU consumption by supplying malformed TEI blocks with many unmatched opening tags. Attackers can exploit lazy regex patterns in the read_block method through public APIs like words() and tagged_words() to force repeated rescans and achieve near-quadratic runtime growth.
- Affected
- nltk
- CVSS v4.0 VULNCHECK
- 6.3 MEDIUM
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/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 - CVSS v4.0 GitHub
- 6.3 MEDIUM
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N - CVSS v3.1 VULNCHECK
- 3.7 LOW
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L - EPSS
- 0.37% chance of exploitation in the next 30 days, 29th percentile
- Published
- 2026-08-27
- Updated
- 2026-08-28
Proof-of-concept exploits (1)
Security advisories
- nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqj
- https://www.vulncheck.com/advisories/nltk-before-3.10.3-regular-expression-denial-of-serv…