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.

Database specific

{
    "cna_assigner": "@huntr_ai",
    "cwe_ids": [
        "CWE-918"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/12xxx/CVE-2026-12372.json"
}

References

Affected packages

Git / github.com/nltk/nltk

Affected ranges

Type

GIT

Repo

https://github.com/nltk/nltk

Events

Introduced

ad9c96ba00a16923ffe917eacf63f1707bfa2d08

Last Affected

ad9c96ba00a16923ffe917eacf63f1707bfa2d08

Database specific

Show details

{
    "cpe": "cpe:2.3:a:nltk:nltk:3.9.4:*:*:*:*:*:*:*",
    "extracted_events": [
        {
            "introduced": "3.9.4"
        },
        {
            "last_affected": "3.9.4"
        }
    ],
    "source": "CPE_STRING"
}

Affected versions

3.*

3.9.4

Database specific

source

"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-12372.json"