What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-22 · updated 2026-10-22
• Weakness: CWE-79

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.

Affected products

• discourse: from 1.9.0.beta2 before 1.9.0.beta13 — fixed in 1.9.0.beta13

How to fix

Upgrade to a fixed version: discourse 1.9.0.beta13. Check the vendor advisory for mitigations.

References

• https://github.com/discourse/discourse/commit/6e37f09b19
• https://github.com/discourse/discourse/commit/a6f2533d38
• 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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