Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
Versions of NLTK before 3.10.3 are affected by a regular-expression denial of service in the Pl196xCorpusReader. An attacker who can supply a malformed TEI-style corpus file, such as one with many unmatched opening tags, can cause quadratic CPU growth when the application calls public reader methods like words() or tagged_words(). Upgrade to NLTK 3.10.3 or later, where this is fixed. Avoid parsing corpus files from untrusted sources until then.
Not analysed yet
We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.
Severity and exploitation
| Score | Rating | CVSS | Vector | Source |
|---|---|---|---|---|
| 6.3 | Medium | 4.0 | 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 | CNA (VulnCheck) |
- CISA KEV Not listed.
- EPSS 0.0037, the 31st percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:38 UTC First seen by agentprime
- 31 Oct 2026, 14:38 UTC Confirmed by OSV
Sources
- GitHub Advisory Database: GHSA-8mpw-7fpc-4gqj
- OSV: GHSA-8mpw-7fpc-4gqj
- github.com/nltk/nltk/security/advisories/GHSA-8mpw-7fpc-4gqj
- nvd.nist.gov/vuln/detail/CVE-2026-81725
- github.com/nltk/nltk/commit/7808692d451b962711005d954859bb83aabcf8fa
- github.com/nltk/nltk
- github.com/nltk/nltk/releases/tag/v3.10.3
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3752.yaml
- www.vulncheck.com/advisories/nltk-before-3.10.3-regular-expression-denial-of-service-via-pl196xcorpusreader