Local root escalation via stdin integer overflow

Integer overflow in Exim 4 before 4.94.2 allows local users to gain root privileges via crafted backslash-terminated stdin lines. get_stdinput appends each continued line to a growable string without bounding its size; repeated input drives the size negative and causes allocation and copy operations to corrupt memory. Exploitation requires local execution and is impractical in the published proof because more than five days of processing were needed to reach the overflow, but successful corruption could provide full root privileges.