CVE-2025-29913: CryptoLib's Crypto_TC_Prep_AAD Has Buffer Overflow Due to Integer Underflow

CryptoLib provides a software-only solution using the CCSDS Space Data Link Security Protocol - Extended Procedures (SDLS-EP) to secure communications between a spacecraft running the core Flight System (cFS) and a ground station. A critical heap buffer overflow vulnerability was identified in the CryptoTCPrepAAD function of CryptoLib versions 1.3.3 and prior. This vulnerability allows an attacker to trigger a Denial of Service (DoS) or potentially execute arbitrary code (RCE) by providing a maliciously crafted telecommand (TC) frame that causes an unsigned integer underflow. The vulnerability lies in the function CryptoTCPrepAAD, specifically during the computation of tcmacstartindex. The affected code incorrectly calculates the MAC start index without ensuring it remains within the bounds of the ingest buffer. When tcmacstartindex underflows due to an incorrect length calculation, the function attempts to access an out-of-bounds memory location, leading to a segmentation fault. The vulnerability is still present in the repository as of commit d3cc420ace96d02a5b7e83d88cbd2e48010d5723.