Vulnerabilities
Misconfiguration
Compliance
CVE Vulnerabilities

CVE-2018-6954

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

Published: Feb 13, 2018 | Modified: Jun 09, 2025
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
7.2 HIGH
AV:L/AC:L/Au:N/C:C/I:C/A:C
RedHat/V2
RedHat/V3
7 MODERATE
CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Ubuntu
MEDIUM
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Additional information
NVDhttps://nvd.nist.gov/vuln/detail/CVE-2018-6954
CWEhttps://cwe.mitre.org/data/definitions/59.html

systemd-tmpfiles in systemd through 237 mishandles symlinks present in non-terminal path components, which allows local users to obtain ownership of arbitrary files via vectors involving creation of a directory and a file under that directory, and later replacing that directory with a symlink. This occurs even if the fs.protected_symlinks sysctl is turned on.

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

NameVendorStart VersionEnd Version
SystemdSystemd_project*237 (including)
SystemdUbuntuartful*
SystemdUbuntubionic*
SystemdUbuntucosmic*
SystemdUbuntudevel*
SystemdUbuntuesm-infra/bionic*
SystemdUbuntuesm-infra/xenial*
SystemdUbuntuxenial*

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

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