CVE-2026-55872: GYM One admin user list is vulnerable to stored cross-site scripting
GYM One is open-source gym management software for fitness centers, personal trainers, and sports clubs. Prior to 1.4.1, GYM One's admin/users/index.php renders the stored firstname, lastname, and email profile fields into the administrator user list without HTML output encoding. An attacker who can store values in those fields can cause content to execute in an administrator's browser when the administrator visits /admin/users/. The persistent script can access administrator-session data or perform actions with the administrator's privileges until the stored record is removed. This issue is fixed in version 1.4.1.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
GYM Oneto a version that resolves this vulnerability.Fixed in 1.4.1
Event History
Frequently Asked Questions
Who is exposed to this issue?
GYM One deployments running versions before 1.4.1 are affected. The impact occurs when an administrator visits the /admin/users/ user-list page containing a malicious stored profile record.
What does an attacker need to exploit it?
The attacker needs the ability to store crafted content in a user's firstname, lastname, or email profile field. They also need an administrator to load the affected user-list page.
What can the injected script do?
It can execute in the administrator's browser, access administrator-session data, or perform actions using the administrator's privileges. The script remains effective until the malicious stored record is removed.
What should be done if upgrading cannot happen immediately?
Remove or sanitize suspicious values from firstname, lastname, and email profile fields, particularly before administrators visit /admin/users/. Upgrading to version 1.4.1 fixes the issue.