Improper validation of integrity check value in Secure Email Gateway - CVE-2026-20355
Published: September 2, 2026
Vulnerability identifier: #VU146772
CSH Severity: Medium
CVSS v4: 8.2 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-20355
CWE-ID: CWE-354
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to disclose sensitive information.
The vulnerability exists due to insufficient validation of message integrity in the S/MIME decryption functionality when processing intercepted and modified traffic between email gateways. A remote attacker can use a machine-in-the-middle technique to intercept and modify traffic to disclose sensitive information.
Only deployments with S/MIME configured for communication between email gateways are vulnerable.
Affected software
Secure Email Gateway
How to mitigate CVE-2026-20355
Install security update from vendor's website.