A persistent XSS could be injected into the description or the link of a cross reference.
Impact
An attacker could use this vulnerability to force a victim to execute uncontrolled code.
CVSS2 score: 3.5 (AV:N/AC:M/Au:S/C:N/I:P/A:N)
Exploitation
As a project admin create a new cross reference and put <script>alert(1)</script> in the cross reference description and/or the link. You can then go to <tuleap_url>/project/showdetails.php?group_id=<project_id> to trigger the vulnerability.
References
https://cwe.mitre.org/data/definitions/79.html
https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29