Low 3.7Published Aug 27, 2026

CVE-2026-81725NLTK before 3.10.3 Regular Expression Denial of Service via Pl196xCorpusReader

Updated under an hour ago (2026-10-19 06:30 UTC)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 3.7 LOW (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Weakness (CWE): CWE-400
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: VulnCheck
NVD analysis: Analyzed
Record last updated: Aug 28, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

nltk nltk nltk:nltk (from the name)	before 3.10.3; 3.10.3 not affected	CNA record
nltk nltk nltk:nltk	before 3.10.3	NVD

References

https://github.com/nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqjvendor-advisory, exploit
https://www.vulncheck.com/advisories/nltk-before-3.10.3-regular-expression-denial-of-service-via-pl196xcorpusreaderthird-party-advisory

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.