Capability not used to reference varargs array in pure-capability code
Although we don't have a specific test case in our test suite for it (and should!), it appears that the pure-capability varargs ABI for Morello CHERI Clang/LLVM is not using a capability to reference the varargs array. This means that buffer overflows are possible when iterating over the array improperly, which is sometimes and exploitable memory-safety violation.
We do implement this in CHERI-MIPS, but currently have a functional gap for this in CHERI-RISC-V as well. Our open issue is: https://github.com/CTSRD-CHERI/llvm-project/issues/479