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Vulnerability · Published Jul 20, 2026 · Assigned by GitHub_M

CVE-2026-53591FreeScout Vulnerable to Unauthenticated Conversation Thread Injection via HMAC Length Bypass in FetchEmails

High 8.6

In plain English

A high-severity improper authentication in freescout from freescout-help-desk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 19% of all known vulnerabilities).

Severity (CVSS 3.1)8.6High
Exploit odds (30 days)0.3%top 81.5% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

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 (as reported)

VendorProductVersions
freescout-help-desk freescout < 1.8.223

Weakness: CWE-287 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

References