Copyright © 2012 Red Hat, Inc. All rights reserved. Moderate 2026-08-03T07:09:35 nltk: nltk: Installation of attacker-controlled packages due to improper checksum validation 5.3 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N CWE-354

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.

A flaw was found in nltk. The `nltk.downloader.Downloader._download_package()` function does not enforce SHA-256 or MD5 checksum validation before writing and extracting downloaded package bytes to disk. A remote attacker can exploit this by tampering with the package response body through a compromised mirror, malicious proxy, or other source-substitution condition. This can lead to the installation of attacker-controlled package bytes, resulting in malicious content being trusted by downstream users or applications.

Exploit Intelligence Out of support scope exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 Lightspeed Core Fix deferred lightspeed-core/lightspeed-stack-rhel9 Lightspeed Core Fix deferred lightspeed-core/rag-tool-cpu-rhel9 Lightspeed Core Fix deferred lightspeed-core/rag-tool-cuda-12.9-rhel9 OpenShift Lightspeed Fix deferred openshift-lightspeed/lightspeed-ocp-rag-rhel9 OpenShift Lightspeed Fix deferred openshift-lightspeed/lightspeed-service-api-rhel9 OpenShift Lightspeed Fix deferred openshift-lightspeed-tech-preview/lightspeed-rag-tool-rhel9 Red Hat Ansible Automation Platform 2 Out of support scope ansible-automation-platform-25/lightspeed-chatbot-rhel8 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-llama-stack-core-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-ta-lmes-job-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-trustyai-nemo-guardrails-server-rhel9 Red Hat OpenShift AI (RHOAI) Fix deferred rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 https://www.cve.org/CVERecord?id=CVE-2026-12259 https://nvd.nist.gov/vuln/detail/CVE-2026-12259 https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d