Zammad: S/MIME signature verification allows forged sender impersonation

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-84465
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-25 19:17:58 UTC
Updated2026-09-25 19:17:58 UTC
DescriptionZammad is a web based open source helpdesk/customer support system. Prior to 7.1.2, when Zammad checks the digital signature on an incoming S/MIME-signed email, it does not verify that the signing certificate is genuinely trusted, it only checks whether a certificate with a matching name is already stored in the system. An attacker can create their own certificate using the name of a real, previously trusted sender and use it to send a forged email. Zammad will display that email with the same "validly signed" indicator as a genuine message from the real sender, even though the attacker never had access to that sender's actual certificate or private key. This issue is fixed in version 7.1.2.

Risk And Classification

Primary CVSS: v4.0 7.1 HIGH from [email protected]

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/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

Problem Types: CWE-290 | CWE-295 | CWE-347 | CWE-290 CWE-290: Authentication Bypass by Spoofing | CWE-295 CWE-295: Improper Certificate Validation | CWE-347 CWE-347: Improper Verification of Cryptographic Signature

VersionSourceTypeScoreSeverityVector
4.0[email protected]Secondary7.1HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNADECLARED7.1HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
Passive
Confidentiality
None
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:N/SC:N/SI:N/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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Zammad Zammad affected < 7.1.2 Not specified

References

ReferenceSourceLinkTags
github.com/zammad/zammad/commit/9a07d0b8214ac4e8e10c23fce71d613bd0625524 [email protected] github.com
github.com/zammad/zammad/security/advisories/GHSA-m9ff-hjr3-93h4 [email protected] github.com
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