RHEL 9 must enable kernel parameters to enforce discretionary access control on symlinks.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-257802	RHEL-09-213035	SV-257802r925393_rule		Medium

Description
By enabling the fs.protected_symlinks kernel parameter, symbolic links are permitted to be followed only when outside a sticky world-writable directory, or when the user identifier (UID) of the link and follower match, or when the directory owner matches the symlink's owner. Disallowing such symlinks helps mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). Satisfies: SRG-OS-000312-GPOS-00123, SRG-OS-000324-GPOS-00125

Description

By enabling the fs.protected_symlinks kernel parameter, symbolic links are permitted to be followed only when outside a sticky world-writable directory, or when the user identifier (UID) of the link and follower match, or when the directory owner matches the symlink's owner. Disallowing such symlinks helps mitigate vulnerabilities based on insecure file system accessed by privileged programs, avoiding an exploitation vector exploiting unsafe use of open() or creat(). Satisfies: SRG-OS-000312-GPOS-00123, SRG-OS-000324-GPOS-00125

STIG	Date
Red Hat Enterprise Linux 9 Security Technical Implementation Guide	2023-12-01

Details

Check Text ( C-61543r925391_chk )
Verify RHEL 9 is configured to enable DAC on symlinks. Check the status of the fs.protected_symlinks kernel parameter with the following command: $ sudo sysctl fs.protected_symlinks fs.protected_symlinks = 1 If "fs.protected_symlinks " is not set to "1" or is missing, this is a finding. Check that the configuration files are present to enable this kernel parameter. $ sudo /usr/lib/systemd/systemd-sysctl --cat-config \| egrep -v '^(#\|;)' \| grep -F fs.protected_symlinks \| tail -1 fs.protected_symlinks = 1 If "fs.protected_symlinks" is not set to "1" or is missing, this is a finding.

Check Text ( C-61543r925391_chk )

Verify RHEL 9 is configured to enable DAC on symlinks.

Check the status of the fs.protected_symlinks kernel parameter with the following command:

$ sudo sysctl fs.protected_symlinks

fs.protected_symlinks = 1

If "fs.protected_symlinks " is not set to "1" or is missing, this is a finding.

Check that the configuration files are present to enable this kernel parameter.

$ sudo /usr/lib/systemd/systemd-sysctl --cat-config | egrep -v '^(#|;)' | grep -F fs.protected_symlinks | tail -1

fs.protected_symlinks = 1

If "fs.protected_symlinks" is not set to "1" or is missing, this is a finding.

Fix Text (F-61467r925392_fix)
Configure RHEL 9 to enable DAC on symlinks with the following: Add or edit the following line in a system configuration file in the "/etc/sysctl.d/" directory: fs.protected_symlinks = 1 Load settings from all system configuration files with the following command: $ sudo sysctl --system