CVE-2018-1113
Description
Setup in Fedora and Red Hat Enterprise Linux added /sbin/nologin and /usr/sbin/nologin to /etc/shells. This violates security assumptions made by pam_shells and some daemons which allow access based on a user's shell being listed in /etc/shells. Under some circumstances, users which had their shell changed to /sbin/nologin could still access the system.
Statement
Preventing a user from accessing the system without deleting their account is not a simple matter. For utmost security, the account should be deleted. Short of this, we recommend a three-pronged approach:
- change the user's login shell to a harmless command that is not in "/etc/shells" (for example "/bin/false") to prevent commands being run on their behalf
- lock the user's password with "usermod -L" to prevent authentication with pam services
- prevent access to the user's home directory with "chmod 0" or "chown root" and "chmod 700" to prevent authentication with ssh keys etc
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).
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 4.8 | 5.3 | 4.8 |
| Attack Vector | Local | Local | Local |
| Attack Complexity | Low | Low | Low |
| Privileges Required | Low | Low | Low |
| User Interaction | Required | None | Required |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | Low | Low | Low |
| Integrity Impact | Low | Low | Low |
| Availability Impact | Low | Low | Low |
Vector
Red Hat: CVSS:3.0/AV:L/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L
NVD: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
cve.org: CVSS:3.0/AV:L/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:L
Understanding the Weakness (CWE)
Confidentiality
Technical Impact: Read Application Data; Read Files or Directories
An attacker could read sensitive data, either by reading the data directly from a data store that is not properly restricted, or by accessing insufficiently-protected, privileged functionality to read the data.
Integrity
Technical Impact: Modify Application Data; Modify Files or Directories
An attacker could modify sensitive data, either by writing the data directly to a data store that is not properly restricted, or by accessing insufficiently-protected, privileged functionality to write the data.
Access Control
Technical Impact: Gain Privileges or Assume Identity; Execute Unauthorized Code or Commands
When access control checks are not applied consistently - or not at all - an attacker could gain privileges and execute unauthorized code or commands by modifying or reading critical data directly, or by accessing insufficiently-protected, privileged functionality.
Frequently Asked Questions
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