Secure Email and Web
CVE-2026-20355: Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
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.
Published
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Cisco Secure Email 14.0 | See the advisory |
| Cisco Secure Email 13.5 | See the advisory |
| Cisco Secure Email 13.0 | See the advisory |
| Cisco Secure Email 14.2 | See the advisory |
| Cisco Secure Email 13.0 | See the advisory |
| Cisco Secure Email 13.5 | See the advisory |
| Cisco Secure Email 14.2 | See the advisory |
| Cisco Secure Email 14.3 | See the advisory |
| Cisco Secure Email 15.0 | See the advisory |
| Cisco Secure Email 15.0 | See the advisory |
| Cisco Secure Email 15.5 | See the advisory |
| Cisco Secure Email 15.5 | See the advisory |
| Cisco Secure Email 15.5 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 15.0 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 15.5 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 15.5 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 15.0 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 16.0 | See the advisory |
| Cisco Secure Email 16.5 | See the advisory |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
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.
Exploitation
The Cisco Product Security Incident Response Team (PSIRT) is aware that a public announcement is available for the vulnerabilities that are described in this advisory.
The Cisco PSIRT is not aware of any malicious use of the vulnerabilities that are described in this advisory.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 11 Oct 2026.