# CVE-2026-12372: NLTK network URL validation permits SSRF to RFC 6598 shared-address-space hosts

Source: https://junglewise.ai/threats/cve-2026-12372-pysec-2026-3955-a-server-side-request-forgery-ssrf-vulnerability  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-09  
License: CC BY 4.0 with a link back

CVE-2026-12372 · Severity: low · CVSS 3.7 · Published 2026-08-09

A Server-Side Request Forgery (SSRF) vulnerability exists in nltk/nltk versions 3.9.4 and the current develop branch. The `nltk.pathsec.validate_network_url()` function, intended to prevent SSRF by rejecting internal network addresses, fails to reject IPs in the RFC 6598 shared address space (`100.64.0.0/10`). This occurs because Python's `ipaddress` module does not classify such addresses as `is_private` or `is_global`, and the current guard only checks `is_private` and a few explicit categories. An attacker who can influence a URL passed to NLTK's network-loading helpers can exploit this vulnerability to make a strict-mode application send requests to shared-address-space hosts, potentially exposing non-public infrastructure reachable from the application host. The impact is limited to SSRF-style confidentiality exposure, with no code execution claimed.

Technologies: [Nltk](https://junglewise.ai/threats/technologies/nltk-nltk), [nltk (PyPI)](https://junglewise.ai/threats/technologies/nltk). Vendors: [Nltk](https://junglewise.ai/threats/vendors/nltk), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-12372 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-12372 being exploited in the wild.

**How severe is CVE-2026-12372?** Low severity, with a CVSS score of 3.7, published 9 August 2026.

**Which products and versions are affected?** nltk (PyPI) < 3.10.0, ECOSYSTEM:introduced=0,fixed=3.10.0, ECOSYSTEM:introduced=0,last_affected=3.9.4.

**Is there a fix for CVE-2026-12372?** Yes. nltk (PyPI): upgrade to 3.10.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2026-12372?** Check whether you run Nltk or nltk (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- nltk (PyPI): upgrade to 3.10.0 or later

  ```sh
  pip install "nltk>=3.10.0"
  ```


## Affected products

- Nltk
- nltk (PyPI) < 3.10.0, ECOSYSTEM:introduced=0,fixed=3.10.0, ECOSYSTEM:introduced=0,last_affected=3.9.4

## Identifiers

- CVE-2026-12372
- GHSA-2jhm-w3mp-jcwr
- PYSEC-2026-3955

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