CVE-2026-18756: Humhub

High severity, CVSS 7.2. EPSS: 0.5% chance of exploitation in the next 30 days.

HumHub Community Edition 1.18.4 contains a reflected cross-site scripting vulnerability in the Space membership-request workflow. An attacker can place attacker-controlled button configuration in the options query-string parameter of space/membership/request-membership-form, lure an authenticated non-member into submitting the legitimate membership request form, and cause the server to return JavaScript containing attacker-controlled code.

Affected products

• Humhub Humhub: version 1.18.4 only

Published 2026-08-19. Last modified 2026-08-28.