CVE-2026-27444
Published: 04 March 2026
Summary
CVE-2026-27444 is a high-severity Interpretation Conflict (CWE-436) vulnerability in Seppmail Seppmail. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 11.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Deeper analysis
CVE-2026-27444 is a vulnerability in SEPPmail Secure Email Gateway versions prior to 15.0.1, where the software incorrectly interprets email addresses in email headers. This misinterpretation creates a conflict with other mail infrastructure components, enabling attackers to fake the apparent source of an email or decrypt its contents. The issue, published on 2026-03-04, carries a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N) and maps to CWE-436 (Interpretation Conflict).
The vulnerability can be exploited by unauthenticated remote attackers over the network with low attack complexity and no user interaction required. Exploitation allows manipulation of email integrity, such as spoofing the sender's identity to bypass trust mechanisms or decrypting protected emails by leveraging the interpretation discrepancy between SEPPmail and downstream mail systems.
SEPPmail's advisory in the release notes for version 15.0 at https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure addresses the vulnerability. Mitigation requires upgrading to SEPPmail Secure Email Gateway version 15.0.1 or later to correct the header interpretation logic.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-9380
Vulnerability details
SEPPmail Secure Email Gateway before version 15.0.1 incorrectly interprets email addresses in the email headers, causing an interpretation conflict with other mail infrastructure that allows an attacker to fake the source of the email or decrypt it.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Public-facing SEPPmail gateway vulnerability allows unauthenticated remote exploitation (T1190) and directly enables sender spoofing via header interpretation conflict to bypass trust (T1672).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly requires timely remediation of the header interpretation flaw in SEPPmail via patching to version 15.0.1 or later.
Mandates validation of email header inputs to prevent misinterpretation conflicts enabling sender spoofing or decryption bypass.
Enforces monitoring and control of email flows at the gateway boundary to block or detect exploitation of header parsing discrepancies.