CVE-2026-20355
Received Received - Intake

S/MIME Decryption Plaintext Recovery in Cisco Secure Email

Publication date: 2026-09-02

Last updated on: 2026-09-02

Assigner: Cisco Systems, Inc.

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.

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Meta Information

Published
2026-09-02
Last Modified
2026-09-02
Generated
2026-09-02
AI Q&A
2026-09-02
EPSS Evaluated
N/A
NVD
CVE-2026-20355
EUVD
EUVD-2026-70211

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
cisco secure_email *

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-345 The product does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.

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Executive Summary

This vulnerability involves flaws in the S/MIME decryption process of Cisco Secure Email. Attackers can exploit these flaws by intercepting and modifying traffic between email gateways using a machine-in-the-middle technique. This allows them to recover plaintext from encrypted email messages due to insufficient validation of message integrity.

Impact Analysis

If exploited, this vulnerability could allow an attacker to read encrypted email messages, potentially exposing sensitive information such as confidential communications or data. This could lead to privacy breaches or unauthorized access to protected information.

Compliance Impact

This vulnerability could lead to non-compliance with data protection regulations like GDPR or HIPAA, as it may result in unauthorized access to personal or health information. Organizations using affected Cisco Secure Email systems could face legal penalties or reputational damage.

Mitigation Strategies

Update Cisco Secure Email to the latest patched version to address the S/MIME decryption vulnerabilities. Monitor network traffic for unusual activity or man-in-the-middle attempts between email gateways. Disable S/MIME decryption if not required.

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