CVE-2026-20355
Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
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.
Weakness: CWE-345
Affected products
| Vendor | Product | Category | Matched by |
|---|---|---|---|
| Cisco | Cisco Secure Email Gateway | Email Security | cna-assigner |
Vendor-reported products (1)
- Cisco · Cisco Secure Email
Vendor advisory
cisco-sa-esa-smime-disc-dzw4rEdY
Cisco Secure Email Secure/Multipurpose Internet Mail Extensions Ciphertext Decryption Vulnerabilities
Cisco’s rating: Medium (advisory CVSS 5.9) · Published Sep 2, 2026 · updated Sep 8, 2026 (revision 1.1)
Bug IDs: CSCwu28362 , CSCwu28364
The vendor’s rating applies to the whole advisory and can differ from this CVE’s own CVSS severity. Where this comes from