FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to version 1.8.223, an unauthenticated attacker can inject messages into any existing support conversation by sending a single email to the helpdesk's public address with a crafted In-Reply-To header. No credentials, tokens, or prior access are required. The injected message is rendered in the agent UI as a legitimate customer reply, the conversation is automatically reopened, and the last_reply_from field is set to the attacker's identity. Version 1.8.223 contains a fix.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:LI:HA:L8.6/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:LAuthentication