Staging Environment: Content and features may be unstable or change without notice.
Advisory details: github_osv / GHSA-4xw3-jf9x-x7mf
Advisory ID github_osv/GHSA-4xw3-jf9x-x7mf
Aliases
Summary Duplicate Advisory: Downloader.download follows hardlinks and overwrites outside-root files ## Duplicate Advisory This advisory has been withdrawn because it is a duplicate of GHSA-f794-5jv7-7672. This link is maintained to preserve external references. ## Original Description 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.
Status Published
Exploitability 0.5
Weighted Severity 6.4
Risk 3.2
Affected and Fixed Packages Package Details
Introduced and Fixed Package Commit Patches Package Commit Patches Details
Weaknesses (1)
CWE-59 Improper Link Resolution Before File Access ('Link Following')
System Score Found at
cvssv3.1 7.1 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-4xw3-jf9x-x7mf/GHSA-4xw3-jf9x-x7mf.json
cvssv4 6.9 https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-4xw3-jf9x-x7mf/GHSA-4xw3-jf9x-x7mf.json
generic_textual MODERATE
Reference id Reference type URL
https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672
https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader
CVE-2026-81727 https://nvd.nist.gov/vuln/detail/CVE-2026-81727
No exploits are available.

No EPSS data available for this advisory.

Patch URL
There are no known patches.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-4xw3-jf9x-x7mf/GHSA-4xw3-jf9x-x7mf.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Found at https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/08/GHSA-4xw3-jf9x-x7mf/GHSA-4xw3-jf9x-x7mf.json
Attack Vector (AV) Attack Complexity (AC) Attack Requirements (AT) Privileges Required (PR) User Interaction (UI) Vulnerable System Impact Confidentiality (VC) Vulnerable System Impact Integrity (VI) Vulnerable System Impact Availability (VA) Subsequent System Impact Confidentiality (SC) Subsequent System Impact Integrity (SI) Subsequent System Impact Availability (SA)

network

adjacent

local

physical

low

high

none

present

none

low

high

none

passive

active

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

high

low

none

There are no SSVC decisions available.