Cross-mailbox customer modification via unchecked customer lookup
Published Apr 21, 2026 · Updated Apr 21, 2026
Improper authorization in FreeScout before 1.8.214 allows remote authenticated users to modify hidden customers across mailboxes. ConversationsController's processPhoneCustomer() trusts a submitted customer_id, fetches that record directly, and adds the supplied to_email alias without checking whether the agent can view the customer. Exploitation requires a non-admin agent who can create phone conversations and APP_LIMIT_USER_CUSTOMER_VISIBILITY=true; it binds a hidden customer to an accessible mailbox and changes that customer's email data.
Summary
What happened
Improper authorization in FreeScout before 1.8.214 allows remote authenticated users to modify hidden customers across mailboxes. ConversationsController's processPhoneCustomer() trusts a submitted customer_id, fetches that record directly, and adds the supplied to_email alias without checking whether the agent can view the customer. Exploitation requires a non-admin agent who can create phone conversations and APP_LIMIT_USER_CUSTOMER_VISIBILITY=true; it binds a hidden customer to an accessible mailbox and changes that customer's email data.
The record
- CVE
- CVE-2026-40591
- Published
- Apr 21, 2026
- Updated
- Apr 21, 2026
- Vendor
- FreeScout
- Product
- FreeScout
- Classifications
- CWE-639, T1565.001
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Apr 21, 2026CVE publishedPublication date reported by the CVE source.
- Apr 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 1.8.214
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GitHub advisory cross-mailbox customer modification proof of conceptfunctional · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo