unshield: Tests fail with 'possible traversal attack'

I’m trying to build/test unshield on Alpine Linux (with musl libc), and all of the bundled tests fail. I’ve included the output from running the following manually (as found in the baldur gate test sh script):

./build/src/unshield -D 3 -d extract1 x data1.cab

Output:

unshield_fail.log