SB2026101345 - Information disclosure in Microsoft Exchange Server

Description

This security bulletin contains information about 1 vulnerability.

1) Weak Authentication (CVE-ID: CVE-2026-96940)

CWE-ID: CWE-1390 - Weak Authentication

CVSSv4: 7.1 [CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]

The vulnerability allows a remote user to disclose sensitive information.

The vulnerability exists due to weak authentication in Microsoft Exchange Outlook Web Access (OWA) when handling web requests. A remote user can gain unauthorized access to other users' mailboxes and read email messages and attachments to disclose sensitive information.

Mailbox access is limited to users within the same organization; the vulnerability does not allow access across tenant boundaries.

Remediation

Install update from vendor's website.

References

• https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2026-96940
• https://techcommunity.microsoft.com/blog/exchange/released-september-2026-v2-exchange-server-security-updates/4561718