VDB
CVE-2026-81727
CVE-2026-81727
PUBLISHED
CVSS 6.9 MEDIUM
Reported by VulnCheck · Published August 27, 2026
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.
Risk Scores
CVSS 4.0
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
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| nltk | nltk | 0, 3.10.3 |
| chainguard | open-webui | 0 |
| nltk | nltk | 0, 3.10.3 |
| PyPI | nltk | 0 |
| chainguard | nemo | 0 |
| wolfi | open-webui | 0 |
Timeline
- Aug 27, 2026 Coalition ESS Score
- Aug 27, 2026 CVE Published
- Aug 28, 2026 EPSS Score
- Sep 2, 2026 Security Advisory
- Sep 24, 2026 EPSS Score
- Sep 26, 2026 EPSS Score
- Oct 6, 2026 EPSS Score
- Oct 13, 2026 EPSS Score
- Oct 19, 2026 EPSS Score
- Oct 25, 2026 EPSS Score
- Oct 30, 2026 EPSS Score
References
- GitHub Security Advisory (GHSA-f794-5jv7-7672) vendor-advisory
- VulnCheck Advisory: NLTK before 3.10.3 Hardlink File Overwrite via downloader third-party-advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-81727 advisory
- https://github.com/advisories/GHSA-f794-5jv7-7672 advisory
- https://github.com/nltk/nltk/pull/3797 patch
- https://github.com/nltk/nltk/commit/9e6d5f05902b9aaa1221a0a565448d17a9c9b3e8 patch
- https://github.com/nltk/nltk/releases/tag/v3.10.3 url
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3741.yaml advisory