CVE-2026-29140 PUBLISHED

S/MIME Signature Additional Certificate

Assigner: NCSC.ch
Reserved: 04.03.2026 Published: 02.04.2026 Updated: 02.04.2026

SEPPmail Secure Email Gateway before version 15.0.3 allows an attacker to cause attacker-controlled certificates to be used for future encryption to a victim by adding the certificates to S/MIME signatures.

Metrics

CVSS 4.0

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:H/SI:N/SA:N
CVSS Score: 7.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	High
Attack Complexity	Low	Integrity	Low	Integrity	None
Attack Requirements	None	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	SEPPmail
Product	Secure Email Gateway
Versions	Default: unaffected affected from 0 to 15.0.3 (excl.)

Credits

Andris Suter-Dörig finder
Matteo Scarlata coordinator
Kenny Paterson coordinator

References

https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure-1503

Problem Types

CWE-295 Improper Certificate Validation CWE

Impacts

CAPEC-216 Communication Channel Manipulation