Script execution via request button options
Published Aug 19, 2026 · Updated Aug 19, 2026
Reflected XSS in the Space membership-request workflow in HumHub 1.18.4 allows remote attackers to execute script via the options parameter. MembershipController::actionRequestMembershipForm() accepts request-supplied button options, the form preserves them in a hidden field, and the server later merges attacker-controlled title, URL, and data-action values into button markup that requestMembershipSave.php returns inside JavaScript. Exploitation requires an authenticated non-member victim to open a crafted link and submit the normal membership request form with a valid CSRF token, after which attacker code runs in that user's HumHub origin and can issue same-origin actions with the victim's privileges.
Summary
What happened
Reflected XSS in the Space membership-request workflow in HumHub 1.18.4 allows remote attackers to execute script via the options parameter. MembershipController::actionRequestMembershipForm() accepts request-supplied button options, the form preserves them in a hidden field, and the server later merges attacker-controlled title, URL, and data-action values into button markup that requestMembershipSave.php returns inside JavaScript. Exploitation requires an authenticated non-member victim to open a crafted link and submit the normal membership request form with a valid CSRF token, after which attacker code runs in that user's HumHub origin and can issue same-origin actions with the victim's privileges.
The record
- CVE
- CVE-2026-18756
- Published
- Aug 19, 2026
- Updated
- Aug 19, 2026
- Vendor
- HumHub GmbH & Co. KG
- Product
- HumHub
- Classifications
- CWE-79, T1189
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Aug 19, 2026CVE publishedPublication date reported by the CVE source.
- Aug 19, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=1.18.4
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Fluid Attacks reflected XSS proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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