Android 4.3 and Earlier affected by Critical Code-Execution Flaw

June 28, 2014  By Pierluigi Paganini


A serious code-execution vulnerability in Android 4.3 and earlier was patched with latest KitKat Android Operating System version.

Are you using the Android 4.3 version and you are convinced to be secure? You are unfortunately wrong, because this version of Android and earlier are affected by a critical code-execution vulnerability.

According to data proposed by the Android developer site, KitKat adoption is 13,6%, this means that the majority of Android users is currently at risk; 29 percent of users are on Jelly Bean 4.1, the highest version distribution.
Android KitKat distribution
The disclosure of the Android 4.3 vulnerability was made by the Application Security team at IBM which have discovered the flaw nine months ago. The Experts at  IBM confirmed the presence of a critical code-execution vulnerability that affects the Android mobile devices running versions 4.3 and earlier, an attacker could exploit it to steal sensitive data from the vulnerable devices. 
The security researchers discovered that the stack buffer overflow vulnerability resides in the Android’s KeyStore storage service, which is responsible for storing and securing device’s cryptographic keys.
“A stack buffer is created by the ‘KeyStore::getKeyForName’ method” “This function has several callers, which are accessible by external applications using the Binder interface (e.g., ‘android::KeyStoreProxy::get’). Therefore, the ‘keyName’ variable can be controllable with an arbitrary size by a malicious application,” Hay said. “The ‘encode_key’ routine that is called by ‘encode_key_for_uid’ can overflow the ‘filename’ buffer, since bounds checking is absent.” explained the experts in the blog post.
Android KitKat flaw
Successfully exploiting this vulnerability leads to a malicious code execution under the keystore process. Such code can:
  1. Leak the device’s lock credentials. Since the master key is derived by the lock credentials, whenever the device is unlocked, ‘Android::KeyStoreProxy::password’ is called with the credentials.
  2. Leak decrypted master keys, data and hardware-backed key identifiers from the memory.
  3. Leak encrypted master keys, data and hardware-backed key identifiers from the disk for an offline attack.
  4. Interact with the hardware-backed storage and perform crypto operations (e.g., arbitrary data signing) on behalf of the user.
An attacker can theoretically exploit the vulnerability in the Android 4.3 and earlier versions with a malicious application, but as explained by the experts at work exploit is hard to realize due to the presence of numerous difficulties likes the need to to bypass memory-based protections native to the operating system, including Data Execution Prevention (DEP) and Address Space Layout Randomization (ASLR).
The Data Execution Prevention is an exploit mitigation that is used to prevent execution of malicious code, but the attackers have had success to bypass it using the Return Oriented Programming (ROP) attacks. The ASLR is used to mitigate buffer overflow attacks randomizing the memory locations used by system files and other programs, implementing this technique it is hard to guess the location of a given process.

“However, the Android KeyStore is respawned every time it terminates. This behavior enables a probabilistic approach; moreover, the attacker may even theoretically abuse ASLR to defeat the encoding” states the post.

The experts confirmed that they haven’t seen the flaw being exploited in the wild yet.
Currently Google is distributing the Android KitKat 4.4.4 with build number KTU84P (branch kitkat.-mr21-release), the new update was mainly issued to fix the CCS Injection Vulnerability (CVE-2014-0224).
Don’t waste time … update your device when new version will be available for your mobile.

Pierluigi Paganini

(Security Affairs –  Android 4.3,Code-Execution Flaw)



Pierluigi Paganini
Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.





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