Cisco Secure Email S/MIME Decryption Weakness Enables Plaintext Leakage
CVE-2026-20355 Published on September 2, 2026
Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
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.
Vulnerability Analysis
CVE-2026-20355 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have a high impact on confidentiality, with no impact on integrity and availability.
Weakness Type
Insufficient Verification of Data Authenticity
The software does not sufficiently verify the origin or authenticity of data, in a way that causes it to accept invalid data.
Affected Versions
Cisco Secure Email:- Version 14.0.0-698 is affected.
- Version 13.5.1-277 is affected.
- Version 13.0.0-392 is affected.
- Version 14.2.0-620 is affected.
- Version 13.0.5-007 is affected.
- Version 13.5.4-038 is affected.
- Version 14.2.1-020 is affected.
- Version 14.3.0-032 is affected.
- Version 15.0.0-104 is affected.
- Version 15.0.1-030 is affected.
- Version 15.5.0-048 is affected.
- Version 15.5.1-055 is affected.
- Version 15.5.2-018 is affected.
- Version 16.0.0-050 is affected.
- Version 15.0.3-002 is affected.
- Version 16.0.0-054 is affected.
- Version 15.5.3-022 is affected.
- Version 16.0.1-017 is affected.
- Version 15.5.4-012 is affected.
- Version 16.0.4-016 is affected.
- Version 15.0.5-016 is affected.
- Version 16.0.2-112 is affected.
- Version 16.0.3-044 is affected.
- Version 16.5.0-780 is affected.