What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 8.6 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-07-20 · updated 2026-10-24
• Weakness: CWE-287

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

• freescout-help-desk freescout: before 1.8.223

References

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

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