CVE-2017-18078

Published: 29 January 2018

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.

Notes

mitigated by fs.protected_hardlinks = 1

patch simply refuses to set hardlink file permissions if the
kernel hardening feature is turned off, which may result in
breakage. We will not be releasing an update for this issue as
our default configuration is not vulnerable.

Status

Severity score breakdown

References

• https://www.cve.org/CVERecord?id=CVE-2017-18078
• NVD
• Launchpad
• Debian

Bugs

• https://github.com/systemd/systemd/issues/7736