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

Is it exploited?

Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of 29 Oct 2026.

VulnCheck KEV lists it since 22 Oct 2026. It cites 1 public report, the first from 22 Oct 2026.

• cve.org

How likely is exploitation in the next 30 days?

0.3%

EPSS score, percentile 18.4 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

5.1 Medium

CVSS v4.0 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (2)

Which versions are affected?

Affected

• from 1.9.0.beta2 to before 1.9.0.beta13

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; VulnCheck KEV, as of 30 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 30 Oct 2026. About the data.

Description

Discourse < 1.9.0.beta13 Reflected XSS via /email/unsubscribed

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.

Source: CVE List, as of 30 Oct 2026. About the data.

What to do

Advisories and patches

• Fix Commit (Patch)
• Introducing Commit (Technical description, Patch)

This summary is based on the CVE record as of 30 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

Source: CVE List, as of 30 Oct 2026. About the data.

Timeline