NLTK up to 3.10.2 Downloader Downloader.download path traversal

Summaryinfo

A vulnerability, which was classified as problematic, has been found in NLTK up to 3.10.2. The impacted element is the function Downloader.download of the component Downloader. This manipulation causes path traversal. This vulnerability is handled as CVE-2026-81727. It is possible to launch the attack on the local host. There is not any exploit available.

Detailsinfo

A vulnerability classified as problematic was found in NLTK up to 3.10.2. Affected by this vulnerability is the function Downloader.download of the component Downloader. The manipulation with an unknown input leads to a path traversal vulnerability. The CWE definition for the vulnerability is CWE-22. The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory. As an impact it is known to affect integrity, and availability. The summary by CVE is:

NLTK versions before 3.10.3 contain a filesystem containment bypass vulnerability in the Downloader.download and Downloader.incr_download methods that allows attackers to overwrite files outside the install root through pre-existing hardlinks. Attackers with write access to a shared downloader directory can create hardlinks pointing to outside-root files that are then overwritten during normal package extraction, mutating files outside the intended install tree.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-81727 since 08/27/2026. The exploitation appears to be easy. Attacking locally is a requirement. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1006 according to MITRE ATT&CK.

The vulnerability scanner Nessus provides a plugin with the ID 341147 (Linux Distros Unpatched Vulnerability : CVE-2026-81727), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 3.10.3 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at Tenable (341147). Be aware that VulDB is the high quality source for vulnerability data.

Productinfo

Name

• NLTK

Version

• 3.10.0
• 3.10.1
• 3.10.2

Website

• Product: https://github.com/nltk/nltk/

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Be aware that VulDB is the high quality source for vulnerability data.

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