Summary
When building packages directly from source control, file permissions on the checked-in files are not maintained.
Details
When building packages directly from source control, file permissions on the checked-in files are not maintained. When nfpm packaged the files (without extra config for enforcing its own permissions) files could go out with bad permissions (chmod 666 or 777).
PoC
Create a default nfpm structure.
Within the test folder, create 3 files named chmod-XXX.sh. Each script has file
permissions set corresponding with their file names (chmod-777.sh = chmod 777). Below each
file and permissions can be seen.
$ ls -lart test
total 24
-rwxrwxrwx 1 user group 11 May 19 13:15 chmod-777.sh
-rw-rw-rw- 1 user group 11 May 19 13:16 chmod-666.sh
drwxr-xr-x 5 user group 160 May 19 13:19 .
-rw-rw-r-- 1 user group 11 May 19 13:19 chmod-664.sh
drwxr-xr-x 10 user group 320 May 19 13:29 ..
Below is the snippet nfpm configuration file of the contents of the package. The test folder
and files has no extra config for enforcing permissions.
contents:
- src: foo-binary
dst: /usr/bin/bar
- src: bar-config.conf
dst: /etc/foo-binary/bar-config.conf
type: config
- src: test
dst: /etc/test/scripts
The next step is to create a deb package.
$ nfpm package -p deb # Create dep package
using deb packager...
created package: foo_1.0.0_arm64.deb
When on a Ubuntu VM, install the foo package which was created
$ sudo dpkg -i foo_1.0.0_arm64.deb # Installing deb package within Ubuntu
Selecting previously unselected package foo.
(Reading database ... 67540 files and directories currently installed.)
Preparing to unpack foo_1.0.0_arm64.deb ...
Unpacking foo (1.0.0) ...
Setting up foo (1.0.0) ...
Looking at /etc/test/scripts and viewing the permissions. Permissions are passed exactly the same as the source.
$ ls -lart /etc/test/scripts
total 20
-rwxrwxrwx 1 root root 11 May 22 12:15 chmod-777.sh
-rw-rw-rw- 1 root root 11 May 22 12:16 chmod-666.sh
-rw-rw-r-- 1 root root 11 May 22 12:19 chmod-664.sh
drwxr-xr-x 3 root root 4096 May 22 13:00 ..
drwxr-xr-x 2 root root 4096 May 22 13:00 .
Solution
To prevent world-writable files from making it into the packages, add the ability to override the default permissions of packaged files using a umask config option in the packaging spec file. This feature in nfpm would allow applying a global umask across any files being packaged, therefore, with the correct configuration, preventing world-writable files without needing to list permissions on each and every file in the package
Impact
Vulnerability is https://cwe.mitre.org/data/definitions/276.html
https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Anyone using nfpm for creating packages and not checking/setting file permissions before packaging could result in bad permissions for files/folders.
References
oCHRISo Reporter
caarlos0 Remediation developer
djgilcrease Remediation reviewer
Summary
When building packages directly from source control, file permissions on the checked-in files are not maintained.
Details
When building packages directly from source control, file permissions on the checked-in files are not maintained. When nfpm packaged the files (without extra config for enforcing its own permissions) files could go out with bad permissions (chmod 666 or 777).
PoC
Create a default nfpm structure.
Within the test folder, create 3 files named
chmod-XXX.sh. Each script has filepermissions set corresponding with their file names (
chmod-777.sh=chmod 777). Below eachfile and permissions can be seen.
Below is the snippet nfpm configuration file of the contents of the package. The test folder
and files has no extra config for enforcing permissions.
The next step is to create a deb package.
When on a Ubuntu VM, install the foo package which was created
Looking at
/etc/test/scriptsand viewing the permissions. Permissions are passed exactly the same as the source.Solution
To prevent world-writable files from making it into the packages, add the ability to override the default permissions of packaged files using a umask config option in the packaging spec file. This feature in nfpm would allow applying a global umask across any files being packaged, therefore, with the correct configuration, preventing world-writable files without needing to list permissions on each and every file in the package
Impact
Vulnerability is https://cwe.mitre.org/data/definitions/276.html
https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
Anyone using nfpm for creating packages and not checking/setting file permissions before packaging could result in bad permissions for files/folders.
References