Researchers at German security firm Curesec have identified bugs present in most versions of Android that can allow malicious applications to place phone calls, even when they lack the necessary permissions.
By exploiting these vulnerabilities, rogue apps can get up to such mischief as surreptitiously dialing out to expensive toll services, potentially racking up big charges on unsuspecting customers' phone bills.
The same exploits can also be used to hang up outgoing calls and to send Unstructured Supplementary Service Data (USSD) codes – special, carrier-specific codes that can be used for such things as enabling call forwarding, blocking SIM cards, changing caller anonymization options, and so on.
Even security programs that can revoke permissions from apps provide no protection from these bugs, because the corresponding exploits circumvent the Android permissions system altogether.
"As the app does not have the permission but is abusing a bug, such apps cannot easily protect you from this without the knowledge that this bug exists in another class on the system," the Curesec researchers write.
Many versions of Android are affected. Curesec has identified two different bugs that can be exploited to achieve the same ends – one that's present in newer Android releases and another that's found in older versions.
The first bug, identified as CVE-2013-6272, was introduced in Android 4.1.1 Jelly Bean and it exists in all versions through Android 4.4.2 KitKat. It appears to have been fixed in the latest version, 4.4.4, but almost nobody is running that release yet.
A second bug has been identified in Android 2.3.3 and 2.3.6, both flavors of Gingerbread. That one was fixed in Android 3.0 Honeycomb, but that was a tablet-only release that no longer even charts on Google's Android statistics. Android 4.0 Ice Cream Sandwich also seems to be immune, but only 12.3 per cent of Android devices are running that version.
That leaves nearly 87 per cent of Android users running versions of the OS that may be vulnerable to dialer-manipulating malware.
For each of the two bugs, Curesec has published source code and a proof-of-concept demonstration app that customers can use to test whether their devices are vulnerable.
For newer KitKat phones, the fix is to get upgraded to version 4.4.4 as soon as possible. Device makers and carriers are expected to start rolling out those updates in the coming weeks.
Given handset makers' generally poor track record for upgrading their kit, however, owners of older Android devices now have one more reason to be very cautious about which apps they install. ®