Link following in Natural Language Toolkit - #VU142781
Published: August 15, 2026
Vulnerability identifier: #VU142781
CSH Severity: Low
CVSS v4: 6.9 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N]
CVE-ID: N/A
CWE-ID: CWE-59
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a local user to overwrite files outside the intended install root.
The vulnerability exists due to improper link resolution before file access in nltk.downloader.Downloader.download and nltk.downloader.Downloader.incr_download when installing a package into a downloader root containing a pre-existing hardlink. A local user can place a hardlink inside a writable shared downloader directory so that package extraction writes through it to overwrite files outside the intended install root.
Exploitation requires a writable shared downloader root on the same filesystem as the target file.
Affected software
Natural Language Toolkit
Remediation
Install security update from vendor's website.
Natural Language Toolkit - update to 3.10.3