Is CVE-2026-40591 in the CISA KEV catalog?

No. CVE-2026-40591 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-40591?

CVE-2026-40591 has a CVSS v3 base score of 7.1 (HIGH).

What is the EPSS score for CVE-2026-40591?

CVE-2026-40591 has an EPSS score of 0.21% (11th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2026-40591?

No published fix for CVE-2026-40591 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-40591

HIGH

7.1

CVSS v3

NVD

Description

FreeScout is a free self-hosted help desk and shared mailbox. Prior to version 1.8.214, the phone-conversation creation flow accepts attacker-controlled `customer_id`, `name`, `to_email`, and `phone` values and resolves the target customer in the backend without enforcing mailbox-scoped customer visibility. As a result, a low-privileged agent who can create a phone conversation in Mailbox A can bind the new Mailbox A phone conversation to a hidden customer from Mailbox B and add a new alias email to that hidden customer record by supplying `to_email`. Version 1.8.214 fixes the vulnerability.

CWE-639Authorization Bypass Through User-Controlled Key

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.21%probability of exploitation in 30 days

11thpercentile

Low risk: more likely to be exploited than 11% of all known CVEs.

References

Other references3

Related Vulnerabilities

Other CWE-639 (Authorization Bypass Through User-Controlled Key) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2023-6875	Critical	9.8	90%	-	-
CVE-2024-46982	High	7.5	61%	-	Fix
CVE-2021-45428	Critical	9.8	57%	-	-
CVE-2019-17382	Critical	9.1	54%	-	Fix
CVE-2019-13360	Critical	9.8	24%	-	-
CVE-2023-48783	Medium	5.4	22%	-	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-22.