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Vulnerability record · CVE-2026-53591 · published 20 July 2026

CVE-2026-53591: Improper authentication vulnerability

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.

8.6 CVSS 3.1 High EPSS 0.38% · top 71.2% CWE-287 · Improper authentication Deferred
8.6CVSS 3.1 base score
0.38%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
21 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-53591), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.