What is the CVSS score of CVE-2026-27443?

CVE-2026-27443 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N. EPSS exploitation probability: 0.1%.

How to fix or mitigate CVE-2026-27443?

Within 24 hours: Identify all SEPPmail Secure Email Gateway instances and document current versions in your environment. Within 7 days: Contact SEPPmail for patch availability and deployment timeline; implement email header validation logging to detect suspicious activity. Within 30 days: Deploy patched versions (15.0.1 or later) across all systems; conduct audit of email traffic logs for evidence of header manipulation attempts.

Seppmail CVE-2026-27443

HIGH

Improper Input Validation (CWE-20)

2026-03-04 vulnerability@ncsc.ch

Code Injection Seppmail

7.5

CVSS 3.1 · NVD

View

Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

Access

Craft S/MIME email with malicious headers
Exploit

Send to SEPPmail gateway
Execution

Gateway fails to sanitize protected MIME headers
Impact

Attacker controls trusted headers in delivered message

Vulnerability Assessment

Weakness	CWE CWE-20 OWASP Top 10:2025 A05:2025 - Injection ASVS 5.0 V2 - Validation and Business Logic Input validation, allowlisting
Exploitation Conditions	SEPPmail Secure Email Gateway versions before 15.0.1 with S/MIME processing enabled. No authentication required; remote attacker can send specially crafted S/MIME emails to any configured gateway instance.
Impact	CVSS 7.5 (HIGH). Attack vector: Network. Complexity: Low. Privileges required: None. User interaction: None.
Exploit ScenarioDerived	An attacker could exploit this vulnerability to compromise the affected system.

This Week Schedule remediation this week. Why: HIGH severity (CVSS 7.0-8.9).

No patch listed yet 0.1% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 12, 2026

SEPPmail Secure Email Gateway versions before 15.0.1 fail to properly validate S/MIME message headers, enabling attackers to forge or manipulate email headers and bypass trust mechanisms without authentication. This allows adversaries to spoof trusted senders or inject malicious headers into encrypted messages, potentially facilitating phishing and social engineering attacks. No patch is currently available for affected installations.

Earlier versions of this analysis (1)

v1 Mar 12, 2026 - 22:05 CVSS 7.5

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. [CVSS 7.5 HIGH]

RemediationAI

Monitor vendor advisories for a patch. Restrict network access to the affected service where possible.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

Classified as CWE-20 (Improper Input Validation). Affects Seppmail. 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.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

High

Availability

None

DescriptionCVE.org

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.

Executive ViewAI

Why It Matters

SEPPmail Secure Email Gateway versions before 15.0.1 contain a vulnerability that allows attackers to manipulate email headers in S/MIME protected messages, potentially enabling email spoofing and bypassing security controls. This directly impacts the integrity of email authentication and trust mechanisms across your organization.

Business Impact: High

Compensating Controls

Implement enhanced email header validation and authentication checks (SPF, DKIM, DMARC) at upstream mail servers; enable detailed logging and alerting for S/MIME message processing anomalies; restrict S/MIME email processing to trusted internal senders only if operationally feasible; deploy mail filtering rules to flag messages with suspicious header inconsistencies; consider network segmentation to limit exposure of affected systems until patch is applied.

Threat Intelligence Overview

EPSS Score

0.1%

Top 73% exploitable

Data Quality

3 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV No

Public POC No

EPSS 0.1%

Patch available No

Active threat No

Deciding rule

HIGH severity (CVSS 7.0-8.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Yes

Human Impact

High

Priority Score

Low Medium High Critical

KEV: 0

EPSS: 0

CVSS: +38

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.