CVE-2026-29138
Published: 02 April 2026
Summary
CVE-2026-29138 is a medium-severity LDAP Injection (CWE-90) vulnerability in Seppmail Secure Email Gateway. Its CVSS base score is 6.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 12.1th 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-2026-29138 is a vulnerability in SEPPmail Secure Email Gateway versions prior to 15.0.3. It enables attackers to use a specially crafted email address to claim another user's PGP signature as their own. The issue 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 is linked to CWE-90.
The vulnerability can be exploited by any unauthenticated attacker accessible over the network, requiring low complexity and no user interaction. Successful exploitation results in high integrity impact, allowing the attacker to impersonate another user's PGP signature without affecting confidentiality or availability.
SEPPmail's release notes for version 15.0, available at https://downloads.seppmail.com/extrelnotes/150/ERN15.0.html#seppmail-vulnerability-disclosure-1503, disclose the vulnerability and confirm that it is addressed in version 15.0.3. Security practitioners should update affected SEPPmail Secure Email Gateway installations to version 15.0.3 or later to mitigate the issue.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-18156
Vulnerability details
SEPPmail Secure Email Gateway before version 15.0.3 allows attackers with a specially crafted email address to claim another user's PGP signature as their own.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Vuln in public-facing email gateway enables network exploitation (T1190); crafted address allows PGP signature impersonation (T1656) and email spoofing (T1672) with high integrity impact.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely application of the vendor patch in SEPPmail version 15.0.3 directly remediates the flaw enabling attackers to claim another user's PGP signature via crafted email addresses.
Validating email address inputs in the Secure Email Gateway prevents specially crafted addresses from being processed to impersonate PGP signatures.
Implementing non-repudiation mechanisms ensures PGP signatures are properly bound to the correct user identities, mitigating unauthorized claims of another user's signature.