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Nginx hardening profile

Introduction

This is a hardening profile to help securing nginx by using systemd unit configuration. It’s goal is to restrict what nginx can do and make it harder for any possible vulnerability to be misused.

The rationale for the selected settings is based on the analysis as part of the article Hardening nginx with systemd security features.

Relevant FAQ: How to use systemctl edit to change a service?

Notes

Depending on external components such as PHP, temporary files may need to be made accessible. When possible, define an alternative directory and keep PrivateTmp enabled.

Changes

Version 2

Add PrivateTmp=yes
Changed LockPersonality from ’true’ to ‘yes’
Additional comments

Hardening profile

Important notes

Test this profile first on a non-production system
Reload and restart nginx a few times after applying the new settings
Confirm that there is a master process and workers

Applying this profile

Open the unit file for nginx with the built-in editor.

systemctl edit nginx.service

Copy the following block into the editor. As the profile can change over time, it is suggested to include the link and version. This way changes can easily be compared in the future. Also add your own customizations at the top to simplify the comparison.

################################################################################
# Source: https://linux-audit.com/systemd/hardening-profiles/nginx/
# Profile version: 2 [2024-11-15]
################################################################################
# Customizations:
# - Insert here the changes you made to the profile
################################################################################

[Service]
# ===============================
# Paths
# ===============================
# Deny access to /dev/shm directory, suggested when using MemoryDenyWriteExecute=yes
# Details: https://linux-audit.com/systemd/settings/units/inaccessiblepaths/
InaccessiblePaths=/dev/shm
# Do not allow execution of files, except nginx itself
# Details: https://linux-audit.com/systemd/settings/units/noexecpaths/
NoExecPaths=/
# Details: https://linux-audit.com/systemd/settings/units/execpaths/
ExecPaths=/usr/sbin/nginx /usr/lib
# Allow creation of PID file and writing to log files (access|error).log
# Details: https://linux-audit.com/systemd/settings/units/readwritepaths/
ReadWritePaths=/run /var/log/nginx

# ===============================
# Capabilities and system calls
# ===============================
# Only allow: bind to ports < 1024, change file permissions/ownership so nginx workers can use them
# Details: https://linux-audit.com/systemd/settings/units/capabilityboundingset/
CapabilityBoundingSet=CAP_NET_BIND_SERVICE CAP_CHOWN CAP_DAC_OVERRIDE CAP_SETGID CAP_SETUID
# Only allow the usage of system calls for own hardware platform. Advised when using RestrictAddressFamilies
# Details: https://linux-audit.com/systemd/settings/units/systemcallarchitectures/
SystemCallArchitectures=native
# Define an allow-list filter for system calls
# Details: https://linux-audit.com/systemd/settings/units/systemcallfilter/
SystemCallFilter=@system-service
# Explicit block memfd_create() due to using MemoryDenyWriteExecute=yes
SystemCallFilter=~memfd_create
# Block @mount, suggested as extension to PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=, ProtectKernelTunables=, ProtectControlGroups=, ProtectKernelLogs=, ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and ReadWritePaths=.
SystemCallFilter=~@clock @mount @reboot

# ===============================
# Memory
# ===============================
# Do not allow memory segments to be writable+executable
# Details: https://linux-audit.com/systemd/settings/units/memorydenywriteexecute/
MemoryDenyWriteExecute=yes

# ===============================
# Privileges
# ===============================
# Do not gain new privileges
# Details: https://linux-audit.com/systemd/settings/units/nonewprivileges/
NoNewPrivileges=yes

# ===============================
# Personality
# ===============================
# Do not allow personality switch
# Details: https://linux-audit.com/systemd/settings/units/lockpersonality/
LockPersonality=yes

# ===============================
# Private
# ===============================
# Restrict access to devices in /dev, except for pseudo-devices like /dev/null, /dev/random, /dev/zero
# Details: https://linux-audit.com/systemd/settings/units/privatedevices/
PrivateDevices=yes
# Limit access to temporary directories such as /tmp and /var/tmp by creating a new namespace
# Details: https://linux-audit.com/systemd/settings/units/privatetmp/
PrivateTmp=yes

# ===============================
# Protect and Proc
# ===============================
# Do not allow changing the system clock
# Details: https://linux-audit.com/systemd/settings/units/protectclock/
ProtectClock=yes
# Details: https://linux-audit.com/systemd/settings/units/protectcontrolgroups/
ProtectControlGroups=yes
# No access to home directories
# Details: https://linux-audit.com/systemd/settings/units/protecthome/
ProtectHome=yes
# Do not allow changing the hostname
ProtectHostname=yes
# No access to kernel log ring buffer
# Details: https://linux-audit.com/systemd/settings/units/protectkernellogs/
ProtectKernelLogs=yes
# Do not allow loading kernel modules
# Details: https://linux-audit.com/systemd/settings/units/protectkernelmodules/
ProtectKernelModules=yes
# Don't allow changes to sysctl settings
# Details: https://linux-audit.com/systemd/settings/units/protectkerneltunables/
ProtectKernelTunables=yes
# No access to information about other users in /proc
# Details: https://linux-audit.com/systemd/settings/units/protectproc/
ProtectProc=invisible
# Most of the system paths will no longer be writable
# Details: https://linux-audit.com/systemd/settings/units/protectsystem/
ProtectSystem=strict
# Restricts information from /proc that not directly associated with process management and introspection
# Details: https://linux-audit.com/systemd/settings/units/procsubset/
ProcSubset=pid

# ===============================
# Restrictions
# ===============================
# Limit address families INET/INET6 for IPv4/IPv6, UNIX for local functions such as syslog
# Details: https://linux-audit.com/systemd/settings/units/restrictaddressfamilies/
RestrictAddressFamilies=AF_INET AF_INET6 AF_UNIX
# No access to Linux namespace functionality
# Details: https://linux-audit.com/systemd/settings/units/restrictnamespaces/
RestrictNamespaces=yes
# Realtime scheduling not allowed
# Details: https://linux-audit.com/systemd/settings/units/restrictrealtime/
RestrictRealtime=yes
# Do not allow setting set-user-ID and set-group-ID
# Details: https://linux-audit.com/systemd/settings/units/restrictsuidsgid/
RestrictSUIDSGID=yes

# ===============================
# Sockets
# ===============================
# Block socket bind as the default, then use SocketBindAllow to create allow-list
# Details: https://linux-audit.com/systemd/settings/units/socketbinddeny/
SocketBindDeny=any
# Allow port 80 (HTTP)
# Details: https://linux-audit.com/systemd/settings/units/socketbindallow/
SocketBindAllow=tcp:80
# Allow port 443 (HTTPS)
SocketBindAllow=tcp:443
# Allow port 443 (HTTPS), HTTP/3 with QUIC
SocketBindAllow=udp:443

# ===============================
# Umask
# ===============================
# Create new directories and files with 700/600 file permissions
# Details: https://linux-audit.com/systemd/settings/units/umask/
UMask=0077

Restart the nginx service

systemctl restart nginx.service

After restarting the service, check the status.

systemctl status nginx.service

Last step is checking the service and its log files.

Troubleshooting

All is working? Perfect!

A file mentioned in the hardening profile does not exist on your system
- Adjust the path
- Add a hyphen before optional paths)
Process can't start as it requires additional paths
- Add the paths
- Make sure that paths that needs to be written to are defined in ReadWritePaths
Process can't bind to a port
- Specify port with SocketBindAllow

See troubleshooting a failed systemd unit to learn how to do a more in-depth check of a failing systemd unit.

Did the hardening profile work right away or still some issues? Send a quick message!