apparmor

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Prerequisites

Ensure apparmor daemon is running

$ systemctl status apparmor
$ systemctl start apparmor

Install neccessary tools

$ apt install apparmor-utils

Default firefox profile shipped with Kali Linux

# This profile allows everything and only exists to give the
# application a name instead of having the label "unconfined"

abi <abi/4.0>,
include <tunables/global>

profile firefox /{usr/lib/firefox{,-esr,-beta,-devedition,-nightly},opt/firefox}/firefox{,-esr,-bin} flags=(unconfined) {
  userns,

  # Site-specific additions and overrides. See local/README for details.
  include if exists <local/firefox>
}

1. Generate a starting profile

Creates a profile in /etc/apparmor.d with the naming convention where the slashes (/) are converted to dots (.)

Eg. /usr/bin/firefox -> usr.bin.firefox

$ aa-autodep [path-to-binary]

# eg.
$ aa-autodep /usr/bin/firefox

Default profile

Generated on Kali Linux (Kali 6.12.25-1kali1 (2025-04-30))

usr.bin.firefox

abi <abi/4.0>,

include <tunables/global>

/usr/bin/firefox flags=(complain) {
  include <abstractions/base>
  include <abstractions/bash>

  /usr/bin/dash ix,
  /usr/bin/firefox r,

}

2. Optionally, load the profile using aa-genprof or aa-logprof

The aa-genprof tool uses aa-logprof under the hood to augment the profile

Ubuntu Manpage: aa-logprof - utility for updating AppArmor security profiles

Ubuntu Manpage: aa-genprof - profile generation utility for AppArmor

Generate a new profile according to logs from the specified log file

For /usr/bin/firefox, I used aa-autodep instead of aa-genprof to generate the starting profile. This is because there are too many file reads from firefox (as shown in the log file), thus aa-genprof displays too much output.

$ aa-genprof [executable] --file /path/to/logfile

# eg.
$ aa-genprof /usr/bin/firefox --file /var/log/syslog

Update the existing profile

$ aa-logprof --file /path/to/logfile

# eg.
$ aa-logprof --file /var/log/syslog

3. View the profile and manually edit the configurations

$ cd /etc/apparmor.d

# /usr/bin/firefox -> usr.bin.firefox
$ vim usr.bin.firefox

# ********************************
# ** My current profile

abi <abi/4.0>,

include <tunables/global>

profile firefox /{usr/{bin,lib/firefox{,-esr}},opt/firefox}/firefox{,-esr,-bin}

{
  userns,
  
  #include <abstractions/base> # seems to not be required

  # ~~~~~~~~~~~~~~~~~~~~~
  # ALLOW FIREFOX-ESR FILES
  # ~~~~~~~~~~~~~~~~~~~~~
  /usr/lib/firefox-esr/firefox-esr ix,
  /usr/lib/firefox-esr/glxtest ix,
  /usr/lib/firefox-esr/minidump-analyzer ix,

  # ~~~~~~~~~~~~~~~~~~~~~
  # ALLOW HOME DIR FILES
  # ~~~~~~~~~~~~~~~~~~~~~
  @{HOME}/.local/share/** wrmkix,
  @{HOME}/.config/** wrmkix,
  @{HOME}/.cache/.mozilla/** r,
  @{HOME}/.mozilla/** rwmkix,
 
  # ~~~~~~~~~~~~~~~~~~~~~
  # ALLOW OTHER FILES - to refined: make the file accesses more fine-tuned
  # ~~~~~~~~~~~~~~~~~~~~~
  owner /tmp/** rwkmix, 
  /tmp/firefox-esr/** rwkmix,
  
  /etc/** r,
  /proc/** rw,
  /usr/share/** r,
  /usr/local/share/** r,
  /var/cache/fontconfig/** r,
  /sys/** r,
  /var/** r,
  /dev/** rw,
  owner /run/user/@{uid}/** rw, # owner keyword
  
  # ~~~~~~~~~~~~~~~~~~~~~
  # DENY
  # ~~~~~~~~~~~~~~~~~~~~~
  deny /etc/ssh/** rwkmx,
  deny /etc/passwd rwkmx,
  deny /etc/network/** rwkmx,
  deny /etc/NetworkManager/** rwkmx,
  deny /proc/version r,

  # ~~~~~~~~~~~~~~~~~~~~~
  # CAPABILITY
  # ~~~~~~~~~~~~~~~~~~~~~
  capability sys_admin,
  capability sys_chroot,

  # ~~~~~~~~~~~~~~~~~~~~~
  # NETWORK
  # ~~~~~~~~~~~~~~~~~~~~~
  # network netlink raw, # ~raw sockets - requested by Firefox, but not neccessary
  network inet dgram, # UDP
  network inet stream, # TCP

  # Site-specific additions and overrides. See local/README for details.
  include if exists <local/firefox>
}

 
  # deny /proc/version rwlk,
}
# ********************************

Abstractions

The include <abstraction/...> statement allows reusable profile configurations to be defined. They can be found under /etc/apparmor.d/abstractions .

Profile language

Refer to the documentation for more information on what each statement in the profile configuration mean:

QuickProfileLanguage · Wiki · AppArmor / apparmorGitLab

4. Load and enforce the profile

# Load the profile
$ apparmor_parser -r /etc/apparmor.d/[profile]
# enforce the profile
$ aa-enforce [profile]

# eg.
$ apparmor_parse -r /etc/apparmor.d/usr.bin.firefox
$ aa-enforce /usr/bin/firefox

apparmor_parser

Used to compile the profile (understood by the kernel), and load it into the kernel

• -r flag: To update the existing profile in the kernel

This flag is required if an AppArmor definition by the same name already exists in the kernel; used to replace the definition already in the kernel with the definition given on standard input.

Ubuntu Manpage: apparmor_parser - loads AppArmor profiles into the kernel

5. View the status

$ aa-status

apparmor modules are loaded
XX profiles are loaded.
X profiles are in enforce mode.
    ...
    /usr/bin/firefox
    ...
...
    ...

6. View the logs and manually update the profile

After loading the profile into the kernel, we can run the application (controlled by apparmor in enforce mode), and view the logs for any DENIED error messages:

Install required packages

$ apt install rsyslog
$ systemctl start rsyslog

Filter the logs

$ cat /var/log/syslog | grep [executable]  | grep -P T[timestamp]\w* 

# eg. firefox at 1800 HRS
$ cat /var/log/syslog | grep firefox  | grep -P T18:\w* 
$ cat /var/log/syslog | grep firefox  | grep DENIED | grep -P T18:\w* # view DENIED 

View the logs in real-time

$ tail -f /var/log/syslog | grep -E 'firefox|DENIED' 

From the error messages, we can update the profile linked to the executable accordingly.

Example

Given the following error message:

xxxx : apparmor="DENIED" operation="open" class="file" profile="firefox" name="/proc/xxxx/xxxx" ... comm="firefox-esr" requested_mask="w" denied_mask="w" 

The message tells us that firefox-esr is trying to write (w) to /proc/xxxx/xxxx, but got DENIED access. To fix this issue, we can add a rule to the profile:

/proc/** w,

For more information on file pattern matching, refer to the documentation on the File Globbing section:

QuickProfileLanguage · Wiki · AppArmor / apparmorGitLab

7. Verify the apparmor configurations

...

Example

Given the configurations in place for firefox, we can now open up a window and check if the file restrictions are working.

...

8. Other useful commands

Refer to the documentation link at the start of this page

$ aa-disable 
$ aa-audit
...