Viber for Windows up to 13.2.0.39 does not properly quote its custom URI handler. A malicious website could launch Viber with arbitrary parameters, forcing a victim to send an NTLM authentication request, and either relay the request or capture the hash for offline password cracking. NOTE: this issue exists because of an incomplete fix for CVE-2019-12569.

An exploitable information disclosure vulnerability exists in the 'Secret Chats' functionality of Rakuten Viber on Android 9.3.0.6. The 'Secret Chats' functionality allows a user to delete all traces of a chat either by using a time trigger or by direct request. There is a bug in this functionality which leaves behind photos taken and shared on the secret chats, even after the chats are deleted. These photos will be stored in the device and accessible to all applications installed on the Android device.

Viber through 11.7.0.5 allows a remote attacker who can capture a victim's internet traffic to steal their Viber account, because not all Viber protocol traffic is encrypted. TCP data packet 9 on port 4244 from the victim's device contains cleartext information such as the device model and OS version, IMSI, and 20 bytes of udid in a binary format, which is located at offset 0x14 of this packet. Then, the attacker installs Viber on his device, initiates the registration process for any phone number, but doesn't enter a pin from SMS. Instead, he closes Viber. Next, the attacker rewrites his udid with the victim's udid, modifying the viberudid file, which is located in the Viber preferences folder. (The udid is stored in a hexadecimal format.) Finally, the attacker starts Viber again and enters the pin from SMS.

A vulnerability in Viber before 10.7.0 for Desktop (Windows) could allow an attacker to execute arbitrary commands on a targeted system. This vulnerability is due to unsafe search paths used by the application URI. An attacker could exploit this vulnerability by convincing a targeted user to follow a malicious link. Successful exploitation could cause the application to load libraries from the directory targeted by the URI link. The attacker could use this behavior to execute arbitrary commands on the system with the privileges of the targeted user, if the attacker can place a crafted library in a directory that is accessible to the vulnerable system.