CVE-2026-20355 Cisco Secure Email S/MIME Ciphertext Decryption Vulnerabilty
An attacker can recover plaintext from encrypted emails via MITM attacks due to insufficient integrity validation in Cisco Secure Email.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-20355?
CVE-2026-20355 is a medium-severity vulnerability in Cisco Secure Email, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-345
Which versions are affected by CVE-2026-20355?
How do I fix CVE-2026-20355?
No fix has been published for CVE-2026-20355 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-20355 being exploited?
There is no known exploitation of CVE-2026-20355 in the wild and no public exploit code.
Sources
Also known as GHSA-4rjc-g85j-x387.