CVE-2026-27443
Published: 04 March 2026
Summary
CVE-2026-27443 is a high-severity Improper Input Validation (CWE-20) vulnerability in Seppmail Seppmail. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 28.3th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
Threat & Defense at a Glance
Threat & Defense Details
Likely Mitigating ControlsAI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Security testing and developer training directly verify and enforce proper input validation, reducing exploitability of injection and malformed-data weaknesses.
Security testing and evaluation at multiple SDLC stages directly detects missing or flawed input validation, with the required remediation process ensuring fixes are applied.
Directly implements checks on information inputs to reject invalid data before processing.
Spam protection mechanisms perform filtering and detection on inbound/outbound messages, directly compensating for missing or weak input validation of unsolicited content.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
The CVE describes remote exploitation of a public-facing email security gateway via crafted S/MIME emails (directly matching T1190). Successful exploitation enables header manipulation/spoofing that bypasses security controls and misleads recipients (directly matching T1672).
NVD Description
SEPPmail Secure Email Gateway before version 15.0.1 does not properly sanitize the headers from S/MIME protected MIME entities, allowing an attacker to control trusted headers.
Deeper analysisAI
CVE-2026-27443 affects SEPPmail Secure Email Gateway versions prior to 15.0.1, where the software fails to properly sanitize headers from S/MIME protected MIME entities. This improper input validation (CWE-20) enables an attacker to manipulate trusted headers within these entities. The vulnerability 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), indicating high severity due to its network accessibility, low attack complexity, and lack of required privileges or user interaction.
An unauthenticated attacker can exploit this vulnerability remotely by sending a specially crafted email containing S/MIME protected MIME entities with unsanitized headers. Successful exploitation allows the attacker to control trusted headers, resulting in high integrity impact without affecting confidentiality or availability. This could enable header spoofing or injection, potentially bypassing email security controls or misleading recipients and administrators.
The vendor's advisory in the release notes for version 15.0 at https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure details the vulnerability disclosure and recommends upgrading to SEPPmail Secure Email Gateway 15.0.1 or later to mitigate the issue.
Details
- CWE(s)