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.

CVSS 3.1

6.5CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS

0.1% chance of exploitation in the next 30 days; higher than 0% of CVEs (scores of 2026-10-25)

CWE

CWE-494

Published

2026-08-03

Modified

2026-10-23

Record from

the NVD, synced 2026-10-24

Affected

• nltk:nltk

Packages (OSV)

References

• https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d

Check your stackJSON