CVE-2026-18756 HumHub Community Edition 1.18.4-pl1 - Reflected XSS in Space membership request button rendering
Attackers can inject JavaScript via query parameters in HumHub's membership request form, potentially hijacking user sessions or executing code.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-18756?
CVE-2026-18756 is a high-severity cross-site scripting vulnerability in HumHub, published on 19 Aug 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-79
Which versions are affected by CVE-2026-18756?
How do I fix CVE-2026-18756?
No fix has been published for CVE-2026-18756 yet. Limit exposure of the affected software until one is available.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-18756 being exploited?
There is no known exploitation of CVE-2026-18756 in the wild and no public exploit code.