driftregion iso14229 through 0.9.0 contains an integer underflow and downstream out-of-bounds read in the Handle_0x27_SecurityAccess function in iso14229.c that allows a remote unauthenticated attacker to crash a UDS server and potentially read memory past the receive buffer by sending a single-byte 0x27 SecurityAccess request that follows any earlier well-formed 0x27 message.