A vulnerability has been discovered in Android that affects how cross-signed certificates are handled. No current Android release correctly handles these certificates, which are created when two certificates are signed with a looped certificate chain (certificate A signs certificate B; certificate B signs certificate A).
When a specially-constructed malformed certificate is introduced into an Android device (either by a new app being installed or by importing a certificate), the system may behave in unexpected ways. It may either slow down or hang the device until it is forced to reboot.
The vulnerability is caused by two common used classes in the Android framework – the JarFile and KeyStore classes. Any Android features implicitly or explicitly using the either of two classes may be at the risk to be attacked by cross-signed certificates.
- Android commonly used class JarUtils(./libcore/luni/src/main/java/org/apache/harmony/security/utils/JarUtils.java) – These may be used by the JarFile It is used to verify a jar package’s certificates and signature files. Unfortunately, the JarUtils class cannot properly deal with a loop certificate chain and falls into endless loop. The problem happens in all Android versions.
- Android externalKeyStore providers’ classes (Such as ./external/bouncycastle/src/main/java/org/bouncycastle/jce/provider/JDKPKCS12KeyStore.java) – These are used to process PKCS#12 file for the Android KeyStore. If the PKCS#12 file contains a loop certificate chain, the processing in the codes will also fall into endless loop.
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