aerc before 93bec0d allows directory traversal in commands/msgview/open.go because of direct path concatenation of the name of an attachment part,
https://git.sr.ht/~rjarry/aerc/commit/93bec0de8ed5ab3d6b1f01026fe2ef20fa154329
https://git.sr.ht/~rjarry/aerc/commit/2bbe75fe0bc87ab4c1e16c5a18c6200224391629