CVE-2026-81725
NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader
CVSS Score
3.7
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-400 |
| Vendor | nltk |
| Product | nltk |
| Published | Aug 27, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low
Affected Versions
nltk / nltk
0 < 3.10.3