CVE-2026-20355

Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty

Published Sep 2, 2026 CVSS 3.1 · 5.9 Medium EPSS < 1% KEV · Not listed

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.

Affected Products

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Cisco

Cisco Secure Email

unknown

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

No data.

Vendor Product Versions

Cisco

Secure Email

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

Remediation

No solution or workaround provided in the CVE record

Tracking

Advisories

No advisories available

Metrics

No CVSS v4.0

Attack Vector Network

Attack Complexity High

Privileges Required None

Scope Unchanged

Confidentiality Impact High

Integrity Impact None

Availability Impact None

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

Exploit prediction score: < 1% (0.203% probability within 30 days)

Exploitation none

Automatable no

Technical Impact partial

References

Link	Providers
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY

History

Sep 8, 2026 6:30 PM Scoring metrics updated View changes

Type	Values Removed	Values Added
Metrics		ssvc `{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}`

Sep 3, 2026 3:45 PM First appearance in the feed. Affected vendors updated View changes

Type	Values Removed	Values Added
First Time appeared		Cisco Cisco secure Email
Vendors & Products		Cisco Cisco secure Email

Sep 2, 2026 4:30 PM Description updated. Title updated. Weaknesses updated. Added references. Scoring metrics updated View changes

Type	Values Removed	Values Added
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.
Title		Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
Weaknesses		CWE-345
References		https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY
Metrics		cvssV3_1 `{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'}`