CVE Vulnerabilities

CVE-2017-18078

Improper Link Resolution Before File Access ('Link Following')

Published: Jan 29, 2018 | Modified: Nov 07, 2023
CVSS 3.x
7.8
HIGH
Source:
NVD
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CVSS 2.x
4.6 MEDIUM
AV:L/AC:L/Au:N/C:P/I:P/A:P
RedHat/V2
RedHat/V3
6.7 MODERATE
CVSS:3.0/AV:L/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H
Ubuntu
LOW

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.

Weakness

The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

Affected Software

Name Vendor Start Version End Version
Systemd Systemd_project * 237 (excluding)
Systemd Ubuntu artful *
Systemd Ubuntu devel *
Systemd Ubuntu esm-infra-legacy/trusty *
Systemd Ubuntu esm-infra/xenial *
Systemd Ubuntu trusty *
Systemd Ubuntu trusty/esm *
Systemd Ubuntu xenial *

Potential Mitigations

  • Follow the principle of least privilege when assigning access rights to entities in a software system.
  • Denying access to a file can prevent an attacker from replacing that file with a link to a sensitive file. Ensure good compartmentalization in the system to provide protected areas that can be trusted.

References