# CVE-2026-12372 — nltk nltk/nltk

> As of 2026-08-09, CVE-2026-12372 is a LOW-severity vulnerability in nltk nltk/nltk, CVSS v3.1 3.7, EPSS 0.2% (17.4th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-12372 as of 2026-08-09; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-08-09

## What is CVE-2026-12372?

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.

The record classifies CVE-2026-12372 under weakness class [CWE-918](https://intel.threadlinqs.com/cwe/CWE-918). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 57 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 3.7 — LOW (`CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **EPSS (FIRST):** 0.2% probability of exploitation in the next 30 days, higher than 17.4% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 2.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-09

## Is CVE-2026-12372 being exploited?

It currently carries a trending score of 34 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **nltk**: nltk/nltk

## How to fix CVE-2026-12372

No vendor patch reference has been recorded for CVE-2026-12372 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-12372

No threat campaign in the Threadlinqs corpus currently references CVE-2026-12372, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on 2026-08-11. This product uses the NVD API but is not endorsed or certified by the NVD.

**Other references**

- [huntr.com](https://huntr.com/bounties/2911b643-571c-42e4-b0c2-9a1fa6f491db)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-12372
Full detection coverage and IOCs for threats exploiting CVE-2026-12372 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp