Stack Buffer Overflow in Capstone SStream_concat via vsnprintf

Executive Summary

This vulnerability in Capstone versions 6.0.0-Alpha5 and prior involves an unchecked return value from the vsnprintf function in SStream_concat. A malicious use of cs_opt_mem.vsnprintf can cause SStream's index to become negative or exceed its bounds, leading to a stack buffer underflow or overflow when subsequent writes occur.

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Impact Analysis

The vulnerability can lead to a stack buffer underflow or overflow, which may allow an attacker with limited privileges to cause memory corruption. This can potentially result in information disclosure, integrity compromise, or denial of service.

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Mitigation Strategies

Update Capstone to a version later than 6.0.0-Alpha5 that includes the fix from commit 2c7797182a1618be12017d7d41e0b6581d5d529e to prevent the stack buffer underflow/overflow issue.

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Detection Guidance

This vulnerability can be detected by compiling Capstone with AddressSanitizer (ASan) instrumentation and running a test program that uses a custom vsnprintf function returning -1 to trigger the stack buffer underflow/overflow. The test function 'test_underflow_in_sstream' simulates this condition and can reveal crashes or memory corruption indicative of the vulnerability. Specifically, you can build Capstone with ASan enabled (e.g., using clang with -fsanitize=address) and run the provided proof-of-concept or test code that exercises the SStream_concat function with a malicious cs_vsnprintf implementation. There are no specific network detection commands since the vulnerability is local and requires local code execution or plugin loading. Example commands might include: 1) Cloning the Capstone repo and checking out the vulnerable version. 2) Compiling with ASan: `clang -fsanitize=address -g -o test test.c` 3) Running the test executable to observe crashes. This approach detects the vulnerability by triggering the unsafe behavior during execution rather than network scanning. [1, 2]

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