CVE-2026-53591
FreeScout Vulnerable to Unauthenticated Conversation Thread Injection via HMAC Length Bypass in FetchEmails
CVSS Score
8.6
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-287 |
| Vendor | freescout-help-desk |
| Product | freescout |
| Published | Jul 20, 2026 |
| Last Updated | Jul 20, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
Low
Affected Versions
freescout-help-desk / freescout
< 1.8.223