Cisco Secure Email up to 16.5.0-780 S/MIME Decryption missing encryption

Summaryinfo

A vulnerability classified as problematic was found in Cisco Secure Email. Affected by this vulnerability is an unknown functionality of the component S/MIME Decryption. The manipulation results in missing encryption. This vulnerability is cataloged as CVE-2026-20355. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Cisco Secure Email. Affected is an unknown function of the component S/MIME Decryption. The manipulation with an unknown input leads to a missing encryption vulnerability. CWE is classifying the issue as CWE-311. The product does not encrypt sensitive or critical information before storage or transmission. This is going to have an impact on confidentiality. CVE summarizes:

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.

The advisory is shared for download at sec.cloudapps.cisco.com. This vulnerability is traded as CVE-2026-20355 since 10/08/2025. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/02/2026). The MITRE ATT&CK project declares the attack technique as T1600.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-70211). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• Cisco

Name

• Secure Email

Version

• 13.0.0-392
• 13.0.5-007
• 13.5.1-277
• 13.5.4-038
• 14.0.0-698
• 14.2.0-620
• 14.2.1-020
• 14.3.0-032
• 15.0.0-104
• 15.0.1-030
• 15.0.3-002
• 15.0.5-016
• 15.5.0-048
• 15.5.1-055
• 15.5.2-018
• 15.5.3-022
• 15.5.4-012
• 16.0.0-050
• 16.0.0-054
• 16.0.1-017
• 16.0.2-112
• 16.0.3-044
• 16.0.4-016
• 16.5.0-780

License

• commercial

Website

• Vendor: https://www.cisco.com/

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Once again VulDB remains the best source for vulnerability data.

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