What is the CVSS score of CVE-2026-53591?

CVE-2026-53591 has a CVSS 3.1 base score of 8.6 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:L. EPSS exploitation probability: 0.2%.

Which versions of FreeScout are affected by CVE-2026-53591?

FreeScout self-hosted help desk (versions prior to 1.8.223) is vulnerable to unauthenticated message injection allowing attackers to forge customer replies in support conversations without…. A patch is available.

How to fix or mitigate CVE-2026-53591?

Within 24 hours, audit support conversations from the past 30 days for anomalous customer replies and implement email gateway filtering to block messages with forged In-Reply-To headers. Within 7 days, enable enhanced logging on message ingestion in FreeScout, require agent verification before responding to reopened conversations, and evaluate isolating the help desk from external email if operationally feasible. Within 30 days, monitor FreeScout release notes for a patch to version 1.8.223 or later, evaluate emergency vendor support, enforce DKIM/SPF at the mail gateway, and implement customer identity verification workflows for ticket state changes.

FreeScout CVE-2026-53591

EUVD-2026-46081 HIGH

Improper Authentication (CWE-287)

2026-07-20 GitHub_M

Authentication Bypass Freescout Freescout Help Desk

8.6

CVSS 3.1 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

8.6 HIGH

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

vuln.today AI

7.5 HIGH

Single unauthenticated email exploits it remotely (AV:N/AC:L/PR:N/UI:N); impact is pure integrity via spoofed replies (I:H), with no genuine data disclosure or outage (C:N/A:N).

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

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

High

Availability

Low

Lifecycle Timeline

Patch available

Jul 20, 2026 - 21:17 EUVD

Analysis Generated

Jul 20, 2026 - 20:19 vuln.today

CVE Published

Jul 20, 2026 - 19:47 cve.org

HIGH 8.6

DescriptionCVE.org

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.

AnalysisAI

Message injection in FreeScout self-hosted help desk (all versions prior to 1.8.223) lets a remote unauthenticated attacker forge customer replies inside any existing support conversation. By emailing the helpdesk's public intake address with a crafted In-Reply-To header that references a target thread, the attacker's message renders in the agent UI as a legitimate customer reply, silently reopens the conversation, and overwrites last_reply_from with the attacker's identity. No credentials, tokens, or prior access are required (CVSS 8.6); no public exploit has been identified at time of analysis and it is not listed in CISA KEV.

Technical ContextAI

FreeScout is a PHP/Laravel-based open-source help desk and shared inbox that ingests inbound email and threads replies into existing conversations. Threading relies on RFC 5322 message-correlation headers - specifically In-Reply-To (and References) - to attach an incoming email to a prior conversation. The flaw is classed as CWE-287 (Improper Authentication): the mail-ingestion pipeline trusts the attacker-supplied In-Reply-To header to associate a message with a conversation without verifying that the sender is the legitimate customer party to that thread. Because inbound email to a public helpdesk address is unauthenticated by design, and threading headers are fully attacker-controllable, any message can be grafted onto any conversation the attacker can reference. The affected product per CPE is cpe:2.3:a:freescout-help-desk:freescout, all versions up to but not including 1.8.223.

RemediationAI

Vendor-released patch: 1.8.223 - upgrade all FreeScout instances to 1.8.223 or later, which contains the fix for the In-Reply-To threading authentication flaw, and review the advisory at https://github.com/freescout-help-desk/freescout/security/advisories/GHSA-8vm3-wwq4-ggfx. Because exploitation only requires sending email to the public helpdesk address, there is no clean network-level block that preserves functionality, so interim compensating controls are limited. If immediate patching is impossible, instruct agents to treat unexpected conversation reopenings and replies with suspicion and verify anomalous customer replies out-of-band before acting on them, and audit conversations for reopenings or last_reply_from values that do not match the original customer - accepting that this is detective rather than preventive. Restricting who can email the intake address (for example, allowlisting known customer domains at the MTA) reduces exposure but breaks the open-intake model of a public helpdesk, so weigh that trade-off. Upgrading to 1.8.223 is strongly preferred over any workaround.