# Denial of Service in Page Error Handling

Advisory record · `GHSA-4p9g-qgx9-397p`

- **Identifiers:** `GHSA-4p9g-qgx9-397p` · `BIT-typo3-2021-21359` · `CVE-2021-21359` · `PKSA-8svt-p3nh-mpwn` · `PKSA-g918-9bjy-w911`
- **State:** Confirmed
- **Severity:** CVSS 5.9 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-405](https://cwe.mitre.org/data/definitions/405.html) · [CWE-674](https://cwe.mitre.org/data/definitions/674.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md) · [CWE-405](https://agentprime.io/advisories/tag/cwe-405.md)
- **Published:** 23 Mar 2021
- **Updated:** 8 Jul 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 23 Mar 2021, 01:54 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `typo3/cms-core` (Packagist): affected `>=10.0.0, <10.4.14 || >=11.0.0, <11.1.1 || >=9.0.0, <9.5.25`; fixed in `10.4.14`, `11.1.1`, `9.5.25`
- `typo3/cms` (Packagist): affected `>=10.0.0, <10.4.14 || >=11.0.0, <11.1.1 || >=9.0.0, <9.5.25`; fixed in `10.4.14`, `11.1.1`, `9.5.25`

## 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

- 5.9 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.017, the 77th percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the GitHub Advisory Database, published 23 Mar 2021. New records show when each source confirmed them.

## Sources

- [GitHub Advisory Database: GHSA-4p9g-qgx9-397p](https://github.com/advisories/GHSA-4p9g-qgx9-397p)
- [OSV: GHSA-4p9g-qgx9-397p](https://osv.dev/vulnerability/GHSA-4p9g-qgx9-397p)
- <https://github.com/TYPO3/TYPO3.CMS/security/advisories/GHSA-4p9g-qgx9-397p>
- <https://nvd.nist.gov/vuln/detail/CVE-2021-21359>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms-core/CVE-2021-21359.yaml>
- <https://github.com/FriendsOfPHP/security-advisories/blob/master/typo3/cms/CVE-2021-21359.yaml>
- <https://packagist.org/packages/typo3/cms-core>
- <https://typo3.org/security/advisory/typo3-core-sa-2021-005>

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-4p9g-qgx9-397p>, 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-4p9g-qgx9-397p/>. Everything for agents: <https://agentprime.io/llms.txt>.