Reference page — cumulative record through Monday, October 19, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.
AV AC PR UI S C I A CVSS EPSS %ile KEV N L N R U N H N 6.5 .0010 0.9 —
AFFECTED Product Versions Fixed nltk/nltk unspecified – —
TIMELINE Jun 15 Reserved by @huntr_ai Aug 3 Published (CNA: @huntr_ai) Oct 15 RESCORED — CVE-2026-12259 (nltk/nltk). CVSS 5.3 → 6.5 (NVD).
In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.
| Date | Event | Detail |
|---|---|---|
| June 15, 2026 | Reserved | Reserved by @huntr_ai |
| August 3, 2026 | Published | Published (CNA: @huntr_ai) |
| October 15, 2026 | RESCORED | RESCORED — CVE-2026-12259 (nltk/nltk). CVSS 5.3 → 6.5 (NVD). |
| Vendor | Product / Package | Ecosystem | Version introduced | Fixed |
|---|---|---|---|---|
| nltk | nltk/nltk | — | unspecified | — |
Authoritative record: CVE-2026-12259 at cve.org
Vendors: nltk
Weaknesses: CWE-494
This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-12259 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Monday, October 19, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.
