Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty

Summary

CVE	CVE-2026-20355
State	PUBLISHED
Assigner	cisco
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-09-02 17:17:34 UTC
Updated	2026-09-02 19:23:13 UTC
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.

Risk And Classification

Primary CVSS: v3.1 5.9 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS: 0.001490000 probability, percentile 0.043960000 (date 2026-09-06)

Problem Types: CWE-345 | CWE-345 Insufficient Verification of Data Authenticity

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	5.9	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`
3.1	CNA	CVSSV3_1	5.9	MEDIUM	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N`

CVSS v3.1 Breakdown

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Cisco	Cisco Secure Email	affected 14.0.0-698	Not specified
CNA	Cisco	Cisco Secure Email	affected 13.5.1-277	Not specified
CNA	Cisco	Cisco Secure Email	affected 13.0.0-392	Not specified
CNA	Cisco	Cisco Secure Email	affected 14.2.0-620	Not specified
CNA	Cisco	Cisco Secure Email	affected 13.0.5-007	Not specified
CNA	Cisco	Cisco Secure Email	affected 13.5.4-038	Not specified
CNA	Cisco	Cisco Secure Email	affected 14.2.1-020	Not specified
CNA	Cisco	Cisco Secure Email	affected 14.3.0-032	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.0.0-104	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.0.1-030	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.5.0-048	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.5.1-055	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.5.2-018	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.0-050	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.0.3-002	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.0-054	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.5.3-022	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.1-017	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.5.4-012	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.4-016	Not specified
CNA	Cisco	Cisco Secure Email	affected 15.0.5-016	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.2-112	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.0.3-044	Not specified
CNA	Cisco	Cisco Secure Email	affected 16.5.0-780	Not specified

References

Reference	Source	Link	Tags
sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-sm...	[email protected]	sec.cloudapps.cisco.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

Additional Advisory Data

Exploits

CNA: The Cisco Product Security Incident Response Team (PSIRT) is aware that a public announcement is available for the vulnerabilities that are described in this advisory. The Cisco PSIRT is not aware of any malicious use of the vulnerabilities that are described in this advisory.

There are currently no legacy QID mappings associated with this CVE.