When mount.ecrpytfsprivate before version 87-0ubuntu1.2 calls setreuid() it doesn't also set the effective group id. So when it creates the new version, mtab.tmp, it's created with the group id of the user running mount.ecryptfsprivate.
{ "urgency": "not yet assigned" }
"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2011-3145.json"