Vulnerability · Published Apr 2, 2026 · Assigned by NCSC.ch
CVE-2026-29143S/MIME Decryption Impersonation
High 7.8
In plain English
A high-severity improper input validation in Secure Email Gateway from SEPPmail. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities).
Severity (CVSS 4.0)7.8High
Exploit odds (30 days)0.3%top 82.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
SEPPmail Secure Email Gateway before version 15.0.3 does not properly authenticate the inner message of S/MIME-encrypted MIME entities, allowing an attacker to control trusted headers.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| SEPPmail | Secure Email Gateway | 0 – before 15.0.3 |
Weakness: CWE-20 · Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:H/SA:N