CVE-2017-20290

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.

CVSS 4.0

5.1CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

CVSS 3.1

6.1CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

EPSS

0.3% chance of exploitation in the next 30 days; higher than 18% of CVEs (scores of 2026-10-25)

CWE

CWE-79

Published

2026-10-22

Modified

2026-10-22

Record from

the NVD, synced 2026-10-22

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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