CVE-2020-0306 in Android
Summary
by MITRE
In LLVM, there is a possible ineffective stack cookie placement due to stack frame double reservation. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation.Product: AndroidVersions: Android-11Android ID: A-139666480
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Analysis
by VulDB Data Team • 09/18/2020
The vulnerability identified as CVE-2020-0306 resides within the LLVM compiler infrastructure and represents a critical stack protection mechanism flaw that undermines the effectiveness of stack canaries. This issue specifically manifests in the context of Android 11 systems where the compiler's stack frame allocation process creates a scenario of double reservation, fundamentally compromising the security guarantees provided by stack cookies. The vulnerability stems from how the LLVM compiler generates code for stack frame management, particularly when handling functions that require stack canary protection. When the compiler encounters certain code patterns, it may reserve stack space twice for the same function's stack frame, creating a situation where the stack canary placement becomes ineffective due to overlapping memory regions. This double reservation effectively neutralizes the stack canary's ability to detect buffer overflows and stack corruption attacks that typically exploit the canary's value to prevent exploitation.
The technical flaw operates at the binary code generation level where LLVM's optimization passes fail to properly account for stack frame allocation when multiple memory reservation operations occur within the same function context. This creates a scenario where the stack canary is positioned in memory locations that are either overwritten by subsequent stack operations or are not properly protected due to the overlapping reservation. The vulnerability is classified under CWE-129 as an Improper Limitation of a Pathname to a Restricted Directory, though more accurately reflects a memory corruption issue in stack management. The flaw is particularly dangerous because it affects the fundamental security mechanism designed to prevent stack-based buffer overflow exploits, which are a common attack vector in privilege escalation scenarios. The double reservation creates predictable memory layout issues where the stack canary value may be accessible through memory manipulation techniques that would normally be prevented by proper stack protection.
The operational impact of this vulnerability extends to local privilege escalation scenarios where an attacker with no additional execution privileges can potentially exploit the ineffective stack canary to gain elevated system privileges. The vulnerability is particularly concerning in Android environments where applications may be running with different privilege levels, and the stack canary protection is meant to prevent unauthorized code execution. The exploitation process does not require user interaction, making it particularly dangerous as it can be triggered automatically during normal system operation. This means that any application or service running on the affected Android 11 system could potentially be exploited to achieve privilege escalation without requiring additional attack vectors or user engagement. The vulnerability essentially undermines the compiler-level security protections that are supposed to prevent exploitation of memory corruption vulnerabilities.
Mitigation strategies for CVE-2020-0306 primarily focus on updating the affected Android system to versions that contain fixes for the LLVM compiler stack frame allocation issues. The recommended approach involves patching the Android 11 system with the latest security updates from the Android security bulletin, which typically include fixes for LLVM compiler issues. Organizations should also implement monitoring for any unusual stack behavior or memory access patterns that might indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation" and specifically addresses the use of compiler-level vulnerabilities to bypass system protections. Additionally, security teams should consider implementing memory protection mechanisms such as stack canary validation checks, address space layout randomization, and other exploit mitigation techniques that can provide additional defense in depth. The fix typically involves ensuring proper stack frame reservation handling within the LLVM compiler passes, preventing the double reservation scenario that leads to ineffective stack canary placement, thereby restoring the intended security guarantees of stack protection mechanisms.