Attacker is able to determine if the provided username exists (and it's valid) using Request New Password feature, based on the response time.
https://otrs.com/release-notes/otrs-security-advisory-2022-09/
Source: Mitre, NVD
Published: 2022-06-13
Updated: 2022-06-22
Base Score: 5
Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:N/A:N
Severity: Medium
Base Score: 5.3
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS: 0.00275