CVE-2026-12259
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.
Scoring
- Severity
- MEDIUM
- CVSS base score
- 5.3
- CVSS vector
- CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N
- EPSS probability
- 0.10%
- CWE
- CWE-494
- Published
- 2026-08-03
- Last modified
- 2026-08-03
Affected products
- nltk nltk/nltk
Weakness type
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