CVE-2026-53591: Freescout-Help-Desk Freescout

High severity, CVSS 8.6. EPSS: 0.4% chance of exploitation in the next 30 days.

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.

Affected products

• Freescout-Help-Desk Freescout: before 1.8.223 (fixed in 1.8.223)

Published 2026-07-20. Last modified 2026-07-21.