# Natural Language Toolkit (NLTK): DNS-rebinding SSRF filter bypass in nltk.pathsec.urlopen (nltk.download / nltk.data.load) defeats ENFORCE mode

Advisory record · `GHSA-qvv7-cg9c-w4x3`

- **Identifiers:** `GHSA-qvv7-cg9c-w4x3` · `CVE-2026-12075` · `PYSEC-2026-3583`
- **State:** Confirmed
- **Severity:** CVSS 8.6 High
- **Critical:** No
- **Weakness (CWE):** [CWE-918](https://cwe.mitre.org/data/definitions/918.html)
- **Tags:** [Server-side request forgery (SSRF)](https://agentprime.io/advisories/tag/ssrf.md)
- **Published:** 31 Jul 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 31 Jul 2026, 16:51 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `nltk` (PyPI): affected `<3.10.0`; fixed in `3.10.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> GHSA-qvv7-cg9c-w4x3 affects nltk versions before 3.10.0, where the nltk.pathsec SSRF filter can be bypassed with DNS rebinding. The filter checks the IP a hostname resolves to, but the actual connection resolves the hostname again, so an attacker controlling DNS can pass validation with a public address and connect to an internal or loopback address, even in ENFORCE mode. The attacker can then read full responses from internal services and cloud metadata endpoints. Upgrade nltk to 3.10.0 or later.

Written 4 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.6 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N`, from GitHub Advisory Database

- **CISA KEV:** Not listed.
- **EPSS:** No score.

## Timeline

- 31 Oct 2026, 14:29 UTC: First seen by agentprime
- 31 Oct 2026, 14:29 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-qvv7-cg9c-w4x3)

## Sources

- [GitHub Advisory Database: GHSA-qvv7-cg9c-w4x3](https://github.com/advisories/GHSA-qvv7-cg9c-w4x3)
- [OSV: GHSA-qvv7-cg9c-w4x3](https://osv.dev/vulnerability/GHSA-qvv7-cg9c-w4x3)
- <https://github.com/nltk/nltk/security/advisories/GHSA-qvv7-cg9c-w4x3>
- <https://github.com/nltk/nltk>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-qvv7-cg9c-w4x3>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-qvv7-cg9c-w4x3/>. Everything for agents: <https://agentprime.io/llms.txt>.