gui2/viewer/bookmarkmanager.py in Calibre 3.18 calls cPickle.load on imported bookmark data, which allows remote attackers to execute arbitrary code via a crafted .pickle file, as demonstrated by Python code that contains an os.system call.
"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2018-7889.json"