Machine-written summary
Summary written by Claude Haiku from the source advisory. Not reviewed by a person.
NLTK versions before 3.9.3 do not verify the integrity of packages fetched by its downloader before extracting them. An attacker who can intercept or tamper with the download, such as through a man-in-the-middle position, a race on a shared filesystem, or DNS poisoning, could get malicious content installed. Upgrade to NLTK 3.9.3 or later. The source gives few details on the exact exploit conditions.
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 |
|---|---|---|---|---|
| 5.3 | Medium | 3.0 | CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N | CNA (@huntr_ai) |
- CISA KEV Not listed.
- EPSS 0.0010, the 1st percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.
Timeline
- 31 Oct 2026, 14:08 UTC First seen by agentprime
- 31 Oct 2026, 14:08 UTC Confirmed by OSV
Sources
- GitHub Advisory Database: GHSA-5wp5-5229-5g6q
- OSV: GHSA-5wp5-5229-5g6q
- github.com/nltk/nltk/security/advisories/GHSA-5wp5-5229-5g6q
- nvd.nist.gov/vuln/detail/CVE-2026-12259
- github.com/nltk/nltk/pull/3449
- github.com/nltk/nltk/commit/0e26734a61094b628d93e26dc18dd7302567ac46
- github.com/nltk/nltk
- github.com/nltk/nltk/releases/tag/3.9.3
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3729.yaml
- huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d
- www.vulncheck.com/advisories/nltk-before-missing-post-download-integrity-verification