Red Hat Bugzilla – Bug 1539758
CVE-2017-18078 systemd: Unsafe handling of hard links allowing privilege escalation
Last modified: 2018-01-29 19:42:20 EST
systemd-tmpfiles in systemd before 237 attempts to support ownership/permission changes on hardlinked files even if the fs.protected_hardlinks sysctl is turned off, which allows local users to bypass intended access restrictions via vectors involving a hard link to a file for which the user lacks write access, as demonstrated by changing the ownership of the /etc/passwd file. Upstream bug: https://github.com/systemd/systemd/issues/7736 Upstream patch: https://github.com/systemd/systemd/commit/5579f85663d10269e7ac7464be6548c99cea4ada
Created systemd tracking bugs for this issue: Affects: fedora-all [bug 1539977]
Statement: Red Hat Product Security has rated this issue as having Moderate security impact. This issue is not exploitable in the default configuration Red Hat Enterprise Linux. This issue is not currently planned to be addressed in future updates. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/.
Mitigation: This flaw, and many others like it, is mitigated by enabling hardlink and symlink protections. These protections are enabled by default in Red Hat Enterprise Linux and this vulnerability will only be exploitable if disabled. To ensure your system is protected, check that `fs.protected_hardlinks` is enabled as in the following example: # sysctl fs.protected_hardlinks fs.protected_hardlinks = 1