Open Mercato does not validate regex rules. An attacker with privileges to create the regex rule can add an unsafe regex to a field. When someone provide the proper string it can result in a DoS attack.
This issue was fixed in version 0.6.4.
Exploitability
AV:NAC:LAT:NPR:HUI:NVulnerable System
VC:NVI:NVA:HSubsequent System
SC:NSI:NSA:N6.9/CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NResource Management