CVE-2016-6323 in C Library
Summary
by MITRE
The makecontext function in the GNU C Library (aka glibc or libc6) before 2.25 creates execution contexts incompatible with the unwinder on ARM EABI (32-bit) platforms, which might allow context-dependent attackers to cause a denial of service (hang), as demonstrated by applications compiled using gccgo, related to backtrace generation.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-6323 affects the GNU C Library implementation on ARM EABI 32-bit platforms where the makecontext function fails to create execution contexts that are compatible with the unwinder mechanism. This incompatibility specifically impacts applications that utilize gccgo for compilation and rely on backtrace generation functionality. The issue stems from improper handling of execution context setup during the makecontext function call, which creates a fundamental mismatch between the execution environment and the unwinder's expectations for stack frame unwinding operations.
The technical flaw manifests when applications attempt to generate backtraces using functions like backtrace or backtrace_symbols, which depend on proper execution context management. The makecontext function in glibc versions prior to 2.25 does not correctly initialize the stack frame structure required for the unwinder to properly traverse the call stack. This creates a scenario where the unwinder cannot accurately reconstruct the program execution flow, leading to potential hangs or indefinite blocking during backtrace operations. The vulnerability is particularly significant for ARM-based systems running 32-bit applications that require debugging or error reporting capabilities through stack trace generation.
From an operational perspective, this vulnerability presents a denial of service risk that can affect applications compiled with gccgo on ARM EABI platforms. When an application encounters an error condition requiring backtrace generation, the incompatible execution context causes the system to hang or become unresponsive, effectively rendering the application unusable. The impact extends beyond simple service disruption as it can affect system stability and availability in environments where such applications are critical. Security researchers have noted that while the vulnerability does not appear to enable arbitrary code execution, the denial of service potential makes it a significant concern for systems where application availability is paramount.
The vulnerability aligns with CWE-122, which addresses improper restriction of operations within a restricted environment, and relates to ATT&CK technique T1499.004 for network denial of service. Organizations running ARM-based systems with glibc versions before 2.25 should prioritize updating their systems to address this issue. The recommended mitigation involves upgrading to glibc version 2.25 or later, which includes proper execution context handling for ARM EABI platforms. Additionally, administrators should monitor applications compiled with gccgo for potential hangs during error handling scenarios and implement appropriate application-level monitoring to detect and recover from such situations. The fix ensures that makecontext properly initializes stack frames according to ARM EABI specifications, allowing the unwinder to correctly traverse execution contexts and maintain system stability during backtrace operations.