CVE-2018-6954
Description
It has been discovered that systemd-tmpfiles mishandles symbolic links present in non-terminal path components. In some configurations a local user could use this vulnerability to get access to arbitrary files when the systemd-tmpfiles command is run.
Statement
This flaw affects in particular those systems where custom tmpfiles files are configured (e.g. in /etc/tmpfiles.d). Indeed systemd-tmpfiles installed by system packages set privileges of a directory either to root or to a service specific user and not to interactive users. Even in case they provide one of the vulnerable tmpfiles configuration file (e.g. recursive "Z" type entries), an attacker would still need to perform the attack as the service specific user, which means they would first need to compromise that service.
Moreover, systemd-tmpfiles service is automatically executed only when the system boots, when it is very unlikely an attacker has already a chance to perform any action at all. Otherwise, an attacker would have to wait for an administrator to manually run the systemd-tmpfiles --create command.
Mitigation
There is no known mitigation available.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 7 | 7.8 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | Low | Low | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | High | High | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.0/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Understanding the Weakness (CWE)
Confidentiality,Integrity,Access Control
Technical Impact: Read Files or Directories; Modify Files or Directories; Bypass Protection Mechanism
An attacker may be able to traverse the file system to unintended locations and read or overwrite the contents of unexpected files. If the files are used for a security mechanism then an attacker may be able to bypass the mechanism.
Other
Technical Impact: Execute Unauthorized Code or Commands
Windows simple shortcuts, sometimes referred to as soft links, can be exploited remotely since a ".LNK" file can be uploaded like a normal file. This can enable remote execution.
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