Which versions of Secure Email Gateway are affected by EUVD-2026-18162?

SEPPmail Secure Email Gateway versions before 15.0.3 contain a critical email authentication bypass vulnerability that allows attackers to forge trust indicators and spoof sender identity, directly…. A patch is available.

How to fix or mitigate EUVD-2026-18162?

Within 24 hours: Inventory all SEPPmail deployments and confirm current versions; notify security operations and email administrators of the vulnerability scope. Within 7 days: Apply vendor patch to SEPPmail Secure Email Gateway version 15.0.3 or later across all production instances; verify patch deployment with vendor release notes. Within 30 days: Conduct audit of email logs from affected deployment dates for indicators of forged authentication tags; implement supplementary email authentication policies (DMARC strict enforcement, BIMI) to reduce spoofing risk.

Secure Email Gateway EUVD-2026-18162

Q: What is the CVSS score of EUVD-2026-18162?

EUVD-2026-18162 has a CVSS 4.0 base score of 7.7 (High). CVSS vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X. EPSS exploitation probability: 0.1%.

| CVE-2026-29141 HIGH

Improper Input Validation (CWE-20)

2026-04-02 NCSC.ch

GHSA-239h-g863-fm9x

Authentication Bypass Secure Email Gateway

7.7

CVSS 4.0 · NVD

Severity by source

NVD PRIMARY

7.7 HIGH

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Lifecycle Timeline

Re-analysis Queued

Apr 16, 2026 - 19:07 vuln.today

cvss_changed

Analysis Updated

Apr 16, 2026 - 06:08 EUVD-patch-fix

executive_summary

Re-analysis Queued

Apr 16, 2026 - 05:29 backfill_euvd_patch

patch_released

Patch available

Apr 16, 2026 - 05:29 EUVD

15.0.3

EUVD ID Assigned

Apr 02, 2026 - 09:00 euvd

EUVD-2026-18162

Analysis Generated

Apr 02, 2026 - 09:00 vuln.today

CVE Published

Apr 02, 2026 - 08:34 nvd

HIGH 7.7

DescriptionCVE.org

SEPPmail Secure Email Gateway before version 15.0.3 allows an attacker to bypass subject sanitization and forge tags such as [signed OK].

AnalysisAI

SEPPmail Secure Email Gateway before version 15.0.3 allows remote attackers to bypass subject line sanitization controls and forge authentication tags such as [signed OK], enabling email spoofing attacks that could deceive recipients into trusting fraudulent or malicious messages. The vulnerability affects all versions prior to 15.0.3 and has been publicly disclosed by NCSC.ch; no public exploit code or active exploitation has been independently confirmed at time of analysis.

Technical ContextAI

SEPPmail Secure Email Gateway is a mail security appliance that sanitizes email headers and applies trust indicators (such as [signed OK] tags) to inform recipients about message authentication status. The vulnerability stems from improper input validation (CWE-20: Improper Input Validation) in the subject line processing logic, allowing attackers to inject or manipulate these authentication tags. The affected product is identified by CPE cpe:2.3:a:seppmail:secure_email_gateway:*:*:*:*:*:*:*:*, indicating all versions of the gateway prior to patching are in scope. By forging authentication tags, attackers can circumvent the gateway's core function of providing recipients with reliable indicators of message legitimacy, breaking the trust chain that email security gateways are designed to establish.

RemediationAI

The primary remediation is to upgrade SEPPmail Secure Email Gateway to version 15.0.3 or later. Vendor-released patch: 15.0.3 (available per the Release Notes published at https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure-1503). Organizations should apply this update promptly to restore proper subject line sanitization and prevent tag forgery. Interim workarounds such as additional email filtering rules or user awareness training on suspicious authentication indicators may provide limited defense-in-depth during patch testing, but do not replace the patch. After patching, administrators should monitor email logs for evidence of past exploitation attempts and consider notifying users if suspected phishing campaigns exploiting this bypass have been detected.