Medium [CVE-2026-20354 +1] Cisco Secure Email Secure/Multipurpose Internet Mail Extensions Ciphertext Decryption Vulnerabilities
This medium-severity Cisco advisory covers CVE-2026-20354 and CVE-2026-20355 affecting Secure Email.
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Summary
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.
There are no workarounds that address these vulnerabilities.
- Scope: At the time of publication, these vulnerabilities affected Cisco Secure Email devices if they were running Cisco AsyncOS Software Release 16.5.0 or earlier and had S/MIME configured for communication between email gateways.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- There are no workarounds that address these vulnerabilities.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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