CVE-2026-12259
Improper Input Validation in nltk/nltk
MEDIUM 6.5EPSS 0.1%
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.
- Affected
- nltk · nltk/nltk
- CVSS v3.1 NVD
- 6.5 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N - CVSS v3.1 GitHub
- 5.3 MEDIUM
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N - CVSS v3.0 HUNTR
- 5.3 MEDIUM
CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N - EPSS
- 0.10% chance of exploitation in the next 30 days, 1st percentile
- Published
- 2026-08-03