CVE-2026-84465 Zammad: S/MIME signature verification allows forged sender impersonation
Attackers can forge S/MIME signatures to impersonate trusted senders in Zammad by bypassing certificate trust verification.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-84465?
CVE-2026-84465 is a high-severity vulnerability in zammad, published on 25 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Which versions are affected by CVE-2026-84465?
How do I fix CVE-2026-84465?
No fix has been published for CVE-2026-84465 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-84465 being exploited?
There is no known exploitation of CVE-2026-84465 in the wild and no public exploit code.
Sources
Also known as GHSA-m9ff-hjr3-93h4.