CVE-2026-20355

MEDIUM

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...

Affects 0 products across 1 vendor.

CVSS 3.15.9
EPSS0.2%
Percentile5th
PatchUnknown
CVSS Vector — Plain English Remotely exploitable over the network, high complexity, no authentication required, no user interaction needed, impact contained to the vulnerable component, full confidentiality impact, no integrity impact, no availability impact.
CWE Weakness Definitions
CWE-345: CWE-345
Related Attack Patterns (CAPEC)
CAPEC-142 DNS Cache Poisoning
via CWE-345
CAPEC-218 Spoofing of UDDI/ebXML Messages
via CWE-345
CAPEC-385 Transaction or Event Tampering via Application API Manipulation
via CWE-345
CAPEC-387 Navigation Remapping To Propagate Malicious Content
via CWE-345
CAPEC-388 Application API Button Hijacking
via CWE-345
Show all 12

Mapping is CWE-to-CAPEC per MITRE CAPEC 3.9.

◆ AI Analysis — automated analysis, not human-reviewed

A medium severity vulnerability (CVE-2026-20355) affects the target system. 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 vulnera...

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Frequently Asked Questions
What is CVE-2026-20355?
A medium severity vulnerability (CVE-2026-20355) affects the target system. 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 vulnera...
What is the CVSS score for CVE-2026-20355?
CVE-2026-20355 has CVSS 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N. EPSS: 0.2%.
Is CVE-2026-20355 actively exploited?
No confirmed active exploitation of CVE-2026-20355 as of 2026-09-03.
How do I remediate CVE-2026-20355?
Apply vendor patches for CVE-2026-20355. Monitor Cisco advisories.
What systems are affected by CVE-2026-20355?
CVE-2026-20355 affects: Cisco.
Vulnerability Details
CVE IDCVE-2026-20355
CVSS VectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Published2026-09-02
Last Modified2026-09-02
ICS Relevance55%
Weakness (CWE)
CWE-345
SourceNVD
Official 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.

Source: NIST NVD / MITRE CVE Database

Affected Products
VendorProductFixed Version
Cisco — —
Remediation

No patch URL on record. Monitor vendor security advisories directly.

Threat Intelligence
● Threat Intelligence Validated: September 2026 | Threat Age: 25 Days
CISA KEVNot in KEV catalog
Public ExploitNot confirmed
PoC CodeNot confirmed
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