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.
The MITRE CVE dictionary describes this issue as:
Find out more about CVE-2017-18078 from the MITRE CVE dictionary dictionary and NIST NVD.
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/.
NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.
| CVSS3 Base Score | 6.7 |
|---|---|
| CVSS3 Base Metrics | CVSS:3.0/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H |
| Attack Vector | Local |
| Attack Complexity | High |
| Privileges Required | Low |
| User Interaction | Required |
| Scope | Unchanged |
| Confidentiality | High |
| Integrity Impact | High |
| Availability Impact | High |
| Platform | Package | State |
|---|---|---|
| Red Hat Enterprise Linux 7 | systemd | Will not fix |
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
Vulmon