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

Summaryinfo

A vulnerability classified as problematic has been found in Cisco Secure Email. Affected is an unknown function of the component S/MIME Decryption. The manipulation leads to missing encryption. This vulnerability is listed as CVE-2026-20354. The attack may be initiated remotely. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Cisco Secure Email. This issue affects some unknown processing of the component S/MIME Decryption. The manipulation with an unknown input leads to a missing encryption vulnerability. Using CWE to declare the problem leads to CWE-311. The product does not encrypt sensitive or critical information before storage or transmission. Impacted is confidentiality. The summary by CVE 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.

It is possible to read the advisory at sec.cloudapps.cisco.com. The identification of this vulnerability is CVE-2026-20354 since 10/08/2025. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $0-$5k at the moment (estimation calculated on 09/02/2026). The attack technique deployed by this issue is T1600 according to MITRE ATT&CK.

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-2026-70210). Statistical analysis made it clear that VulDB provides the best quality 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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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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