---
id: CVE-2026-20354
title: Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
summary: "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.\r\n\r\nTh…"
severity: medium
cvss: 5.9
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'
cvssSource: vendor
vendor: Cisco
product: Cisco Secure Email
affected:
  - secure_email 13.0.0-392
  - secure_email 13.5.1-277
  - secure_email 14.0.0-698
  - secure_email 14.2.0-620
  - secure_email 13.0.5-007
  - secure_email 14.3.0-032
  - secure_email 14.2.1-020
  - secure_email 13.5.4-038
  - secure_email 15.0.0-104
  - secure_email 15.0.1-030
  - secure_email 15.5.1-055
  - secure_email 15.5.0-048
  - secure_email 15.5.2-018
  - secure_email 15.0.3-002
  - secure_email 16.0.0-050
  - secure_email 16.0.0-054
  - secure_email 15.5.3-022
  - secure_email 16.0.1-017
  - secure_email 16.0.4-016
  - secure_email 15.5.4-012
  - secure_email 15.0.5-016
  - secure_email 16.0.2-112
  - secure_email 16.0.3-044
  - secure_email 16.5.0-780
published: '2026-09-02'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T11:22:17+00:00'
source: CSAF
sourceUrl: >-
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY
references:
  - url: >-
      https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY
  - url: 'https://software.cisco.com'
tags:
  - csaf
  - vendor-advisory
  - cisco
epss: 0.00161
epssPercentile: 0.04505
ingestedAt: '2026-09-08T15:58:18.533Z'
---

## Overview

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.

There are no workarounds that address these vulnerabilities.

## Vendor advisories

- **cisco-sa-esa-smime-disc-dzw4rEdY** · Cisco · affected: Cisco Secure Email (24 versions) · updated 2026-09-08 · [advisory](https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY)

**Cisco Secure Email Secure/Multipurpose Internet Mail Extensions Ciphertext Decryption Vulnerabilities**. Released 2026-09-02, updated 2026-09-08.

Affected:

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

## Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com