EUVD-2026-67077
GHSA-4xw3-jf9x-x7mf
Severity by source
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
Local access with write access to shared directory required (AV:L/PR:L); no scope change as impact stays within the filesystem authority of the running user (S:U).
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
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
Lifecycle Timeline
2DescriptionCVE.org
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.
AnalysisAI
Filesystem containment bypass in NLTK's Downloader component allows local attackers with write access to a shared download directory to overwrite arbitrary files outside the intended install root by planting hardlinks before a download operation. All NLTK versions prior to 3.10.3 are affected via the Downloader.download and Downloader.incr_download methods, which fail to validate link targets during package extraction. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the attacker have local write access to the NLTK shared downloader directory (AV:L/PR:L per CVSS 4.0 vector) - this is the critical prerequisite. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:H/SC:N/SI:N/SA:N yields a score of 6.9, reflecting local access with low-privilege requirements and high integrity and availability impact on the vulnerable system, but no subsequent-system scope change. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with a local account on a shared HPC cluster creates a hardlink inside the world-writable NLTK data directory (e.g., ~/shared/nltk_data) pointing to a target file on the same filesystem, such as a cron script or application configuration file owned by a higher-privileged service account. When a legitimate user or automated pipeline subsequently runs NLTK's Downloader to fetch a corpus package, the extraction writes package content through the hardlink, silently overwriting the target file with attacker-controlled data. … |
| Remediation | Upgrade NLTK to version 3.10.3 or later, which resolves the hardlink bypass in the Downloader component per the vendor advisory at https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672 and the VulnCheck advisory at https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-59 – Improper Link Resolution Before File Access
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External POC / Exploit Code
Leaving vuln.today