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. In versions 1.3.3 and prior, an unsigned integer underflow in the `Crypto_TC_ProcessSecurity` function of CryptoLib leads to a heap buffer overflow. The vulnerability is triggered when the `fl` (frame length) field in a Telecommand (TC) packet is set to 0. This underflow causes the frame length to be interpreted as 65535, resulting in out-of-bounds memory access. This critical vulnerability can be exploited to cause a denial of service (DoS) or potentially achieve remote code execution. Users of CryptoLib are advised to apply the recommended patch or avoid processing untrusted TC packets until a fix is available.