CVE-2026-20355: cisco cisco secure email

Vulnerability summary

CVE-2026-20355 is a medium (CVSS 5.9) vulnerability in cisco cisco secure email. EPSS estimates a 0.16% chance of exploitation in the next 30 days, higher than 4.8% of scored vulnerabilities.

Timeline

1. 02-09-2026
   PublishedVulnerability first disclosed.
2. 08-09-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-345Insufficient Verification of Data AuthenticityThe product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.