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.
- CVSS 3.0
- 3.7
CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N - EPSS
- 0.3% chance of exploitation in the next 30 days; higher than 17% of CVEs (scores of 2026-10-25)
- CWE
- CWE-918
- Published
- Modified
- Record from
- the NVD, synced
Affected
- nltk:nltk
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-2jhm-w3mp-jcwr | PyPI | nltk | <3.10.0 | 3.10.0 |
| PYSEC-2026-3955 | PyPI | nltk | <=3.9.4 | no fix published |