I recall VoIP vulnerabilities over the years and for many years.
On another note, it is always important to keep in mind that (IT) RISK is the intersection of VULNERABILITY, THREAT & CRITICALITY.
So, even if there is a VULNERABILITY, if there is no real THREAT or CRITICALITY, then RISK is LOW.
For example, for someone who uses VoIP and is not a high profile person or spy or criminal etc who has THREATS and if a VULNERABILITY is exploited, it does not do critical harm (in the case of VoIP threats for most people who use VoIP daily), then the RISK is low.
I've been aware of possible VoIP exploits for many years, but it does not stop me from using the myriad technologies that use VoIP. This especially applies to VoIP technologies which are encrypted. LINE, What's App and I believe Skype are all encrypted and so exploiting these VoIP vulnerabilities are non trivial, as I recall, and so most users who use encrypted VoIP are not at high RISK.
There is also the RISK MITIGATION model, which combines TECHNICAL (LOGICAL) CONTROLS, PHYSICAL CONTROLS AND ADMINISTRATIVE CONTROLS, should be considered as well
Encrypting a VoIP channel is a TECHNICAL CONTROL and having a policy whereas HIGHLY SENSITIVE USERS do not use these apps unless approved is an ADMINISTRATIVE CONTROL.
It is important to keep in mind that RISK MANAGEMENT and RISK MITIGATION is a multidimensional and multifaceted approach, so VULNERABILITIES must be viewed in context to the THREAT and CRITICALITY; and RISK MITIGATION must be viewed in terms of RISK and the "best" combination of controls (ADMIN, TECH, PHYSICAL) based on RISK (and this implies budget as well).
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