# Natural Language Toolkit (NLTK): ReDoS in NLTK ReviewsCorpusReader FEATURES regex

Advisory record · `GHSA-fg7f-2386-8897`

- **Identifiers:** `GHSA-fg7f-2386-8897` · `CVE-2026-12061` · `PYSEC-2026-3582`
- **State:** Confirmed
- **Severity:** CVSS 7.5 High
- **Critical:** No
- **Weakness (CWE):** [CWE-1333](https://cwe.mitre.org/data/definitions/1333.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.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.

> Natural Language Toolkit (NLTK) versions before 3.10.0 are vulnerable to a regular expression denial of service in the ReviewsCorpusReader FEATURES regex. An attacker who can supply a reviews corpus, such as through a service or pipeline that loads untrusted input, can submit one long line without bracketed annotations to cause quadratic CPU consumption that hangs processing. Upgrade to NLTK 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

- 7.5 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`, 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-fg7f-2386-8897)

## Sources

- [GitHub Advisory Database: GHSA-fg7f-2386-8897](https://github.com/advisories/GHSA-fg7f-2386-8897)
- [OSV: GHSA-fg7f-2386-8897](https://osv.dev/vulnerability/GHSA-fg7f-2386-8897)
- <https://github.com/nltk/nltk/security/advisories/GHSA-fg7f-2386-8897>
- <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-fg7f-2386-8897>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-fg7f-2386-8897/>. Everything for agents: <https://agentprime.io/llms.txt>.