CVE-2026-20355: Cisco Secure Email

Medium severity, CVSS 5.9. EPSS: 0.2% chance of exploitation in the next 30 days.

Multiple vulnerabilities in the Secure/Multipurpose Internet Mail Extensions (S/MIME) decryption functionality of Cisco Secure Email could allow an unauthenticated, remote attacker to recover plain text from encrypted email messages. These vulnerabilities are due to insufficient validation of message integrity. An attacker could exploit these vulnerabilities by using a machine-in-the-middle technique to intercept and modify traffic between email gateways. A successful exploit could allow the attacker to obtain plaintext content from the encrypted communication.

Affected products

• Cisco Cisco Secure Email: version 14.0.0-698 only; version 13.5.1-277 only; version 13.0.0-392 only; version 14.2.0-620 only; version 13.0.5-007 only; version 13.5.4-038 only; …

Published 2026-09-02. Last modified 2026-09-02.