Strix
74.9K

CVE-2026-12259

MEDIUMCVSS 6.5/10EPSS 0.10%

Last modified

CVE-2026-12259 is a medium-severity vulnerability rated 6.5/10 on the CVSS scale. 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. EPSS estimates a 0.10% chance of exploitation in the next 30 days.

Description

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.

Metrics

CVSS 3.1
6.5/10

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

CVSS 3.0
5.3/10

CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

EPSS Probability
0.10%

0.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

VendorProductVersions
NltkNltk3.9.4

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is 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.
How severe is CVE-2026-12259?
CVE-2026-12259 has a CVSS score of 6.5/10 (MEDIUM severity). The EPSS model estimates a 0.10% probability of exploitation in the next 30 days.
How do I fix CVE-2026-12259?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

Related CVEs from 2026

View all 2026CVEs →

Are you affected by CVE-2026-12259?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST