S/MIME Decryption Vulnerabilities in Cisco Secure Email

CVE-2026-20355

What is CVE-2026-20355?

Cisco Secure Email contains multiple vulnerabilities in its Secure/Multipurpose Internet Mail Extensions (S/MIME) decryption functionality. These flaws originate from inadequate validation of message integrity, allowing an unauthenticated, remote attacker to exploit them using a machine-in-the-middle approach. By intercepting and manipulating traffic between email gateways, an attacker could potentially retrieve plaintext from encrypted email messages, thereby compromising the confidentiality of sensitive communications.

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