MISP renders the source field of a Galaxy Cluster as a clickable hyperlink whenever the stored value passes PHP's FILTER_VALIDATE_URL validation. Because FILTER_VALIDATE_URL accepts the javascript: URI scheme, a user with galaxy editor privileges on the local instance or on a synced instance could store a javascript: URL as the cluster source.
When another user views the affected Galaxy Cluster and clicks the rendered link, the embedded script executes in the victim's browser context, enabling session hijacking, data exfiltration, or actions performed on behalf of the victim.
Preconditions:
Impact:
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Stored cross-site scripting (XSS) in the victim's browser.
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Potential session theft, credential harvesting, or unauthorized actions within the MISP application.
Affected: <2.5.48.
The fix restricts the rendering of the Galaxy Cluster source field as a hyperlink to only http:// and https:// URLs by adding a regular-expression check (preg_match for ^https?://) in addition to the existing FILTER_VALIDATE_URL validation. This prevents javascript: and other non-HTTP URI schemes from being rendered as clickable links, eliminating the stored XSS vector. The change is applied consistently in both the default theme and the Overmind theme.