CVE intelligence

CVE-2026-20355

Vulnerability intelligence

Published Sep 2, 2026Sources checked Oct 27, 2026

5.9MEDIUMCVSS out of 10

What this means

Review the available evidence

CVE-2026-20355 and is rated Medium severity with a CVSS score of 5.9. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Cisco Security Advisories guidance

Vendor revision: Sep 2, 2026

Vendor remediation details

On September 2, 2026, the Cisco Product Security Incident Response Team (PSIRT) published the following advisories: Cisco Security Advisory CVE ID Security Impact Rating CVSS Base Score Cisco IOS XR Software Security Hardening Release: September 2026 CVE-2026-20277CVE-2026-20278CVE-2026-20280CVE-2026-20279CVE-2026-20276CVE-2026-20275CVE-2026-20274 Critical 9.8 Cisco Nexus 9000 Series Switches Silicon One Remote Code Execution Vulnerability CVE-2026-20212 Critical 9.8 Cisco Desk Phone 9800 Series, IP Phone 7800 and 8800 Series, and Video Phone 8875 with SIP Software Denial of Service Vulnerability CVE-2026-20281 High 7.5 Cisco Secure Email Secure/Multipurpose Internet Mail Extensions Ciphertext Decryption Vulnerabilities CVE-2026-20355CVE-2026-20354 Medium 5.9 To remediate the vulnerabiliti

CISA KEVNot listedBased on the latest collected catalog

EPSS0.2%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-20355?

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.

Source: NVD