Advisory details:
pypa / nltk/PYSEC-2026-597
| Advisory ID | pypa/nltk/PYSEC-2026-597 |
| Aliases |
CVE-2026-12243
GHSA-m42h-3232-vpv3 PYSEC-2026-597 |
| Summary | NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504. The `_UNSAFE_NO_PROTOCOL_RE` regex in `nltk/data.py` checks for literal `../` sequences but fails to account for percent-encoded traversal sequences such as `..%2f`. The `url2pathname()` function decodes these sequences after the validation step, allowing an attacker to bypass the protection. This vulnerability enables an attacker to read arbitrary files accessible to the Python process by controlling the resource name parameter passed to `nltk.data.load()` or `nltk.data.find()`. The issue affects applications that rely on NLTK for resource loading, including NLP web applications, Jupyter notebooks, and CLI tools. The default `pathsec.ENFORCE=False` setting exacerbates the impact by not blocking the file read at the `open()` stage. |
| Status | Published |
| Exploitability | 0.5 |
| Weighted Severity | 6.8 |
| Risk | 3.4 |
| Affected and Fixed Packages | Package Details |
| Introduced and Fixed Package Commit Patches | Package Commit Patches Details |
| There are no known CWE. |
| System | Score | Found at |
|---|---|---|
| cvssv3 | 7.5 | https://github.com/pypa/advisory-database/blob/main/vulns/nltk/PYSEC-2026-597.yaml |
| Reference id | Reference type | URL |
|---|---|---|
| https://github.com/advisories/GHSA-m42h-3232-vpv3 | ||
| 39aa9354-54ca-4e77-96da-580eb1fe6ed1 | Other | https://huntr.com/bounties/39aa9354-54ca-4e77-96da-580eb1fe6ed1 |
No EPSS data available for this advisory.
| Patch URL | |
|---|---|
| There are no known patches. | |
| 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 |
There are no SSVC decisions available.