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CVE-2026-12259

5.3 · MEDIUM

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.

Published Aug 3, 2026CWE-494EPSS 0.10%

Overview

CVE-2026-12259 is a medium-severity vulnerability. It was published on August 3, 2026 and has a CVSS 3.0 base score of 5.3 (MEDIUM).

This vulnerability has a CVSS 3.0 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

Refhuntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d

How CyberStrike helps

Frequently asked questions

What is CVE-2026-12259?

CVE-2026-12259 is a medium-severity vulnerability. It was published on August 3, 2026 and has a CVSS 3.0 base score of 5.3 (MEDIUM).

How severe is CVE-2026-12259?

This vulnerability has a CVSS 3.0 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-12259?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-12259?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-12259 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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