CVE-2026-12372 Server-Side Request Forgery (SSRF) in nltk/nltk
An SSRF vulnerability in NLTK allows attackers to bypass network restrictions and access internal shared-address-space hosts via crafted URLs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-12372?
CVE-2026-12372 is a low-severity server-side request forgery vulnerability in nltk/nltk, published on 9 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-918
Which versions are affected by CVE-2026-12372?
3 open source packages ship an affected version, including nltk. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
nltk PyPI | All versions to 3.9.4 | None |
nltk PyPI | All versions | 3.10.0 |
nltk PyPI | All versions | 3.10.0 |
Linux distribution packages (1)
python-nltk openSUSE:Tumbleweed | All versions | 3.10.2-1.1 |
Products include Nltk Nltk.
How do I fix CVE-2026-12372?
Upgrade nltk to 3.10.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-12372 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-12372 exists.
Other vulnerabilities in nltk/nltk
- CVE-2026-0848 Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading
- CVE-2025-14009 Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution
- CVE-2026-78683 NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
- CVE-2026-79657 NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization
- CVE-2026-79675 NLTK before 3.10.3 JVM Argument Injection via Per-Call Options
Sources
Also known as DEBIAN-CVE-2026-12372, ECHO-55af-12c6-457b, GHSA-2jhm-w3mp-jcwr, MINI-ccv3-jffx-xmp2, PYSEC-2026-3955, UBUNTU-CVE-2026-12372 and 1 more.