AcubeSAT C3 OBC Software Integer Overflow and Truncation in cobs_decode

Vulnerability Overview Vulnerability Name: AcubeSAT C3 OBC Software: Integer Handling Flaw in cobs_decode #6 Vulnerability Type: Integer Overflow or Wraparound (CWE-190) Numeric Truncation Error (CWE-197) Improper Restriction of Operations within the Bounds of a Memory Buffer (CWE-119) Vulnerability Description: An integer handling vulnerability exists in the function of the AcubeSAT OBC (On-Board Computer) software. This function decodes COBS (Consistent Overhead Byte Stuffing) encoded data received via the USART serial interface. The vulnerability stems from two integer handling defects affecting source and destination buffer boundary checks: 1. Signed vs. Unsigned Comparison: Pointer difference ( , signed) is compared with an unsigned integer ( ). On ARM Cortex-M7 (32-bit), this causes the signed pointer difference to be implicitly converted to unsigned. By constructing specific COBS data to manipulate pointer values, an attacker can cause the pointer difference to become negative, bypassing boundary checks and enabling out-of-bounds reads. 2. 8-bit Truncation: When buffer space insufficiency is detected, the code performs subtraction by casting a 32-bit pointer to (8-bit), discarding the upper 24 bits. An attacker can construct COBS data to trigger this truncation, resulting in incorrect calculation of , which in turn leads to buffer overflow or out-of-bounds writes. Affected Components: (Address 0x42696) (Address 0x47228) USART TC message processor ( , Address 0x47269) Attack Vector: Physical access to the USART serial interface ( ) Impact: Potential out-of-bounds read/write Denial of Service Information Leak (Limited exploitability) Impact Scope Denial of Service: An attacker can send malformed COBS data to trigger error conditions in . However, since continues processing subsequent messages after an error, this results only in the rejection of a single malformed message rather than a system-wide DoS. Information Leak: Theoretically, if the truncation vulnerability is triggered, an out-of-bounds read could lead to the leakage of adjacent stack or heap data. However, given the current 128-byte buffer size, this is not achievable. Out-of-bounds Read/Write (Limited Exploitability): The truncation vulnerability may result in an incorrect calculation of under specific conditions, leading to copying more or fewer bytes than intended. This is not exploitable in the current context. Remediation 1. Fix Signed vs. Unsigned Comparison: - Ensure that when comparing pointer differences with unsigned integers, appropriate type casting or comparison logic is used to avoid errors caused by implicit conversion. 2. Fix 8-bit Truncation: - Avoid casting 32-bit pointers to 8-bit types when calculating remaining buffer space. Use appropriate types and logic to ensure correct calculation of pointer differences. 3. Enhance Input Validation: - Implement stricter validation for received COBS data to ensure it conforms to expected formats and length limits. 4. Update Buffer Management: - Re-evaluate buffer sizes and boundary check logic to ensure that out-of-bounds access does not occur when handling data of various sizes. POC Code References CWE-190: Integer Overflow or Wraparound CWE-197: Numeric Truncation Error CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer COBS (Consistent Overhead Byte Stuffing) Specification

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AcubeSAT C3 OBC Software Integer Overflow and Truncation in cobs_decode

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