Tested products: Zemana antimalware v.2.74.2.150 & Zemana antilogger v.2.74.204.150.
Fixed since v.2.74.2.664
About vulnerability:
This vulnerability allowed attackers to get SYSTEM privileges on target machines without user interaction.
Requirements:
1. Attacker must be able to intercept and change content of the POST request to the URL "POST /api/client/settings/"
2. No physical access to the target pc is required.
Details:
Tested products use plain HTTP to receive updates, so attacker can easily change version and appropriate URL to the arbitrary values.
Let’s change update URL to the our simple shell (Pic.0 & appx.1).

Pic.0
Antivirus says that digital signature of the update can’t be verified. But it allows user to run it ANYWAY(pic.1). If user has user rights then it can get SYSTEM rights(Pic.2).


Pic.1. Do you want to run some unknown file with SYSTEM rights?


Pic.2. System rights.

But this alert can be bypassed.
To do it we need copy of the ZAM.exe digital signature. Let’s clone it(Security directory).
Now we have our shell with clone of the Zemana digital signature and it can’t be checked by the OS. (Pic 3).


Pic.3. Incorrect signature.

Now let’s see on the function "ZmnAppUpdater".
We see that result of the SignatureChecker is IGNORED. (Pic.4)


Pic.4. Lost check.

EAX = 0x80096010 (TRUST_E_BAD_DIGEST).

Pic.5. Demo-gif.

CVE-2019-6440