AlmaLinux OS 9 must use reverse path filtering on all IP interfaces.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-269255 | ALMA-09-019820 | SV-269255r1050137_rule | CCI-000366 | medium |
| Description | ||||
| Enabling reverse path filtering drops packets with source addresses that should not have been able to be received on the interface on which they were received. It must not be used on systems that are routers for complicated networks, but is helpful for end hosts and routers serving small networks. | ||||
| STIG | Date | |||
| Cloud Linux AlmaLinux OS 9 Security Technical Implementation Guide | 2026-02-27 | |||
Related Frameworks
4 paths across 3 frameworks
Related Frameworks
NIST 800-531 mapping
CM-6
1.00
- DISA · V1R6 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
NIST 800-1712 mappings
3.4.1
1.00
- DISA · V1R6 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
- NIST · Rev 2 (Feb 2020, errata Jan 2021) · nist_800_171_app_d · equivalent
3.4.2
1.00
- DISA · V1R6 · disa_xccdf · related
- DISA · 2025-01-23 · disa_cci_list · equivalent
- NIST · Rev 2 (Feb 2020, errata Jan 2021) · nist_800_171_app_d · equivalent
CCI1 mapping
CCI-000366
1.00
- DISA · V1R6 · disa_xccdf · related
Details
Check Text (C-269255r1050137_chk)
Verify AlmaLinux OS 9 uses reverse path filtering on all IP interfaces with the following command:
$ sysctl -a | grep -E '\.rp_filter'
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.enp1s0.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
If the returned lines do not all have a value of "1", this is a finding.
Fix Text (F-73187r1049393_fix)
Configure AlmaLinux OS 9 to use reverse path filtering on all IP interfaces.
Create a numbered *.conf file in /etc/sysctl.d/ with the following content:
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.lo.rp_filter = 1
The system configuration files need to be reloaded for the changes to take effect. To reload the contents of the files, run the following command:
$ sysctl --system