Exploiting Android’s Hardened Memory Allocator

Most memory corruptions occur on the heap. To harden userspace applications and prevent heap-based exploitation, Google has developed Scudo. Since Android 11, Scudo has replaced jemalloc as the default heap implementation for all native code on Android. Scudo mitigates exploitation attempts of common heap vulnerabilities.

We present an in-depth study of the security of Scudo on Android by analyzing Scudo’s internals and systematizing Scudo’s security measures. Based on these insights we construct two new exploitation techniques that ultimately trick Scudo into allocating a chunk at an attacker’s chosen address. These techniques demonstrate — given adequate memory corruption primitives — that an attacker can leverage Scudo to gain arbitrary memory write. To showcase the practicality of our findings, we backport an n-day vulnerability to Android 14 and use it to exploit the Android system server.

Our exploitation techniques can be used to target any application using the Scudo allocator. While one of our techniques is fixed in newer Scudo versions, the second technique will stay applicable as it is based on how Scudo handles larger chunks.