Zammad: S/MIME signature verification allows forged sender impersonation

published 2026-09-25 44 d ago modified 2026-09-29 40 d ago also EUVD-2026-87265

cvss: 7.1; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 2%
public exploits: 0; none known

Zammad 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.

Patch / fix

fixed in 1 links 1

zammad zammad 7.1.2

github.com/zammad/zammad@9a07d0b commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 40 d ago (2026-09-29)

Exploit prediction

0.12% chance of exploitation in the next 30 days, higher than 2% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	4.0	7.1	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
CNA	4.0	7.1	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

Affected products

zammad zammad

Classification

Weakness

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

References

Sources

CVE List CVE-2026-84465
NVD CVE-2026-84465

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary