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Cisco Security Updates - September 2026

Roundup of Cisco security advisories published in September 2026.

CVE search metadata

CVE search record: CVE-2026-20354. Severity: medium. CVSS: 5.9. KEV: no. Product: Secure Email. Brief: Cisco Security Updates - September 2026. Brief link: https://feed.craftedsignal.io/briefs/2026-09-cisco-security-updates/

CVE search record: CVE-2026-20355. Severity: medium. CVSS: 5.9. KEV: no. Brief: Cisco Security Updates - September 2026. Brief link: https://feed.craftedsignal.io/briefs/2026-09-cisco-security-updates/

What's new

This roundup covers 2 Cisco security vulnerabilities. None are reported as actively exploited at the time of release. The issues affect Secure Email.

Summary

CVEProductSeverityCVSSEPSSKEVSource
CVE-2026-20354Secure Emailnosource (authoritative)
CVE-2026-20355Secure Emailnosource (authoritative)

CVE-2026-20354

Cisco Secure Email contains multiple vulnerabilities in its S/MIME decryption functionality stemming from insufficient message integrity validation. These flaws allow an unauthenticated, remote attacker to perform machine-in-the-middle attacks to intercept encrypted email traffic, modify it, and subsequently recover the plaintext content of the communications.

Affected products:

  • Secure Email

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY?vs_f=Cisco%20Security%20Advisory%26vs_cat=Security%20Intelligence%26vs_type=RSS%26vs_p=Cisco%20Secure%20Email%20Secure/Multipurpose%20Internet%20Mail%20Extensions%20Ciphertext%20Decryption%20Vulnerabilities%26vs_k=1

Related in this roundup: CVE-2026-20355.

CVE-2026-20355

Cisco Secure Email contains multiple vulnerabilities in its S/MIME decryption functionality stemming from insufficient message integrity validation. These flaws allow an unauthenticated, remote attacker to perform machine-in-the-middle attacks to intercept encrypted email traffic, modify it, and subsequently recover the plaintext content of the communications.

Affected products:

  • Secure Email

Source: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-smime-disc-dzw4rEdY?vs_f=Cisco%20Security%20Advisory%26vs_cat=Security%20Intelligence%26vs_type=RSS%26vs_p=Cisco%20Secure%20Email%20Secure/Multipurpose%20Internet%20Mail%20Extensions%20Ciphertext%20Decryption%20Vulnerabilities%26vs_k=1

Related in this roundup: CVE-2026-20354.