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Secure Email GatewayApplication · Seppmail

CVE-2026-29143

CRITICAL · 9.1 CVSS v3.1 Published 2026-04-02
Fix available
A fix is available. Upgrade to 15.0.3 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
SEPPmail Secure Email Gateway before version 15.0.3 does not properly authenticate the inner message of S/MIME-encrypted MIME entities, allowing an attacker to control trusted headers.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

SEPPmail Secure Email Gateway before version 15.0.3 fails to properly authenticate the inner message content of S/MIME-encrypted MIME entities during decryption processing. This allows an attacker who can inject or manipulate content within an S/MIME-encrypted message to control headers that the system would normally treat as trusted, potentially enabling email spoofing, phishing, or bypass of security filters that rely on header integrity.

MitigationUpgrade SEPPmail Secure Email Gateway to version 15.0.3 or later to obtain the fix for proper inner message authentication in S/MIME handling.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Secure Email GatewayApplication
Affected:< 15.0.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed SEPPmail version
    Locate the SEPPmail installation directory and check the version file or use the product's admin interface to view the current version number. Common locations include /opt/SEPPmail or the admin web UI.
    Affected if The installed version is lower than 15.0.3
  2. Verify S/MIME decryption is enabled
    Check the SEPPmail configuration settings for S/MIME processing. Look for settings related to S/MIME decryption, email processing, or MIME handling in the admin console or configuration files.
    Affected if S/MIME decryption or S/MIME processing is actively enabled on the gateway
  3. Inspect S/MIME processing configuration
    Review the email gateway settings that control how S/MIME-encrypted messages are handled during the decryption phase. Check for any settings related to inner message validation or content authentication.
    Affected if The S/MIME decryption configuration does not validate or authenticate inner message content integrity
  4. Check decryption processing logs
    Review SEPPmail logs related to S/MIME decryption operations. Look for entries showing how inner message headers are processed during decryption.
    Affected if Logs indicate that inner message headers from decrypted S/MIME entities are being trusted without additional validation

You are affected if your SEPPmail Secure Email Gateway version is below 15.0.3 and you have S/MIME decryption processing enabled, as the system will trust inner message headers without proper authentication during decryption.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 15.0.3 or later
Fixed in 15.0.3
Interim mitigation

Upgrade SEPPmail Secure Email Gateway to version 15.0.3 or later to obtain the fix for proper inner message authentication in S/MIME handling.

Recommended fix High confidence

15.0.3

  1. 1. Identify the current version of SEPPmail Secure Email Gateway by accessing the administration interface or running version check commands
  2. 2. Navigate to the official download repository at downloads.seppmail.com
  3. 3. Download SEPPmail Secure Email Gateway version 15.0.3 or later
  4. 4. Follow the vendor's documented upgrade procedure to apply the update
  5. 5. Verify the upgrade was successful by confirming the new version number in the administration interface
  6. 6. Test S/MIME-encrypted message processing to confirm the vulnerability is remediated

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Secure Email Gateway Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA3.0 h
15.0 hours of engineering $2,560
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,096.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-29143 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data