# CVE-2026-81727

## Summary

- **CVE ID:** CVE-2026-81727
- **Severity:** MEDIUM
- **CVSS Score:** 7.1 (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)
- **CWE:** CWE-59
- **Published:** Aug 27, 2026
- **Last Modified:** Aug 27, 2026

## 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.

## Affected Products

- nltk — nltk (0)
- nltk — nltk (3.10.3)

## References

- [CNA](https://github.com/nltk/nltk/security/advisories/GHSA-f794-5jv7-7672)
- [CNA](https://www.vulncheck.com/advisories/nltk-before-3.10.3-hardlink-file-overwrite-via-downloader)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.14%
- **EPSS Percentile:** 3.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._