MISP's RequestHandlerComponent automatically decodes XML request bodies on all write requests. The underlying Xml::build() library contains

MISP's RequestHandlerComponent automatically decodes XML request bodies on all write requests. The underlying Xml::build() library contains a logic error in its readFile guard condition (readFile && http || https), where PHP operator precedence causes the https branch to bypass the readFile check entirely. As a result, a request body containing a bare HTTPS URL is treated as a locator and fetched by the server. Because the cspReport endpoint accepts XML content type and is unauthenticated by design, an unauthenticated remote attacker can send a POST request with a crafted XML body to cause the MISP server to issue an outbound HTTPS request to an arbitrary target reachable from the server.

The attacker does not receive the response body, but can use the vulnerability to probe internal services, trigger actions on internal HTTPS endpoints, or perform timing-based reconnaissance of the server's network environment. 

The vulnerability affects any MISP deployment where the cspReport endpoint is reachable and the server has network access to internal or external HTTPS services.