CVE-2015-3239 in libunwind
Summary
by MITRE
Off-by-one error in the dwarf_to_unw_regnum function in include/dwarf_i.h in libunwind 1.1 allows local users to have unspecified impact via invalid dwarf opcodes.
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Analysis
by VulDB Data Team • 06/13/2022
The vulnerability CVE-2015-3239 represents a critical off-by-one error within the dwarf_to_unw_regnum function located in the include/dwarf_i.h file of libunwind version 1.1. This flaw exists in the handling of DWARF (Debugging With Attributed Record Formats) opcodes, which are essential for stack unwinding operations in debugging and crash analysis tools. The libunwind library serves as a crucial component for implementing stack unwinding in various applications, particularly those requiring detailed backtrace information for debugging or error reporting purposes. When processing invalid DWARF opcodes, the function fails to properly validate array bounds, creating a condition where a single off-by-one error can lead to memory corruption or other unspecified security implications.
The technical implementation of this vulnerability stems from improper boundary checking within the dwarf_to_unw_regnum function, which is responsible for converting DWARF register numbers to unwinding register numbers. This function processes DWARF debugging information that describes the layout and contents of stack frames during program execution. When encountering malformed or invalid DWARF opcodes, the function's array indexing logic does not correctly handle the boundary conditions, potentially causing it to access memory locations beyond the allocated array boundaries. The off-by-one error specifically manifests when the function attempts to map register numbers from DWARF format to the internal unwinding representation, where the indexing calculation fails to account for proper bounds validation. This type of vulnerability falls under the CWE-129 weakness category, which addresses issues related to improper validation of array indices, and can be classified under the ATT&CK technique T1059.007 for execution through command and scripting interpreters.
The operational impact of CVE-2015-3239 extends beyond simple memory corruption, as local users can potentially exploit this vulnerability to achieve arbitrary code execution or system instability. Since libunwind is widely used in system debugging tools, crash handlers, and application monitoring frameworks, an attacker who can control the input to the DWARF processing code can cause the application to behave unpredictably. The unspecified impact mentioned in the description indicates that the consequences could range from denial of service to more severe privilege escalation scenarios, depending on the context in which the vulnerable code executes. Applications that utilize libunwind for stack unwinding during error handling or crash reporting are particularly at risk, as these scenarios often involve processing potentially malicious debugging information. The vulnerability is especially concerning because it operates at a low level within the debugging infrastructure, making detection and prevention challenging.
Mitigation strategies for CVE-2015-3239 should focus on both immediate patching and defensive programming approaches. The most effective solution involves upgrading to a patched version of libunwind that properly validates array bounds during DWARF opcode processing. System administrators should also implement input validation measures that filter or sanitize DWARF debugging information before it reaches the vulnerable function. Additionally, organizations should consider implementing runtime protections such as stack canaries, address space layout randomization, and memory protection mechanisms to reduce the potential impact of exploitation. The vulnerability highlights the importance of thorough input validation in low-level system libraries and demonstrates why robust boundary checking is essential in debugging and stack unwinding components. Security teams should also monitor for similar patterns in other debugging libraries and implement comprehensive testing procedures that include malformed input scenarios to prevent similar vulnerabilities from being introduced in future code releases.