This section describes the security policy of Photon OS.
This the multi-page printable view of this section. Click here to print.
- 1: Default Firewall Settings
- 2: Default Permissions and umask
- 3: Disabling TLS 1.0 to Improve Transport Layer Security
1 - Default Firewall Settings
The design of Photon OS emphasizes security. On the minimal and full versions of Photon OS, the default security policy turns on the firewall and drops packets from external interfaces and applications. As a result, you might need to add rules to iptables to permit forwarding, allow protocols like HTTP, and open ports. You must configure the firewall for your applications and requirements.
The default iptables on the full version have the following settings:
iptables --list Chain INPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED ACCEPT tcp -- anywhere anywhere tcp dpt:ssh Chain FORWARD (policy DROP) target prot opt source destination Chain OUTPUT (policy DROP) target prot opt source destination ACCEPT all -- anywhere anywhere
For more information on how to change the settings, see the man page for iptables.
Although the default iptables policy accepts SSH connections, the
sshd configuration file on the full version of Photon OS is set to reject SSH connections. See Permitting Root Login with SSH.
If you are unable to ping a Photon OS machine, check the firewall rules. To verify if the rules allow connectivity for the port and protocol, change the
iptables commands by using
lsof commands to see the processes listening on ports:
lsof -i -P -n
2 - Default Permissions and umask
umask on Photon OS is set to
When you create a new file with the
touch command as root, the default on Photon OS is to set the permissions to
0640–which translates to
read-write for user,
read for group, and no access for others. Here’s an example:
touch newfile.md stat newfile.md File: 'newfile.md' Size: 0 Blocks: 0 IO Block: 4096 regular empty file Device: 801h/2049d Inode: 316454 Links: 1 Access: (0640/-rw-r-----) Uid: ( 0/ root) Gid: ( 0/ root)
When you create a directory as root, Photon OS sets the permissions to
mkdir newdir stat newdir File: 'newdir' Size: 4096 Blocks: 8 IO Block: 4096 directory Device: 801h/2049d Inode: 316455 Links: 2 Access: (0750/drwxr-x---) Uid: ( 0/ root) Gid: ( 0/ root)
mkdir command uses the umask to modify the permissions placed on newly created files or directories, you can see
umask at work in the permissions of the new directory. Its default permissions are set at
0750 after the umask subtracts
0027 from the full set of open permissions,
Similarly, a new file begins as
0666 if you were to set umask to
0000. But because umask is set by default to
0027, a new file’s permissions are set to
So be aware of the default permissions on the directories and files that you create. Some system services and applications might require permissions other than the default. The
systemd network service, for example, requires user-defined configuration files to be set to
644, not the default of
640. Thus, after you create a network configuration file with a
.network extension, you must run the
chmod command to set the new file’s mode bits to
644. For example:
chmod 644 10-static-en.network
For more information on permissions, see the man pages for
3 - Disabling TLS 1.0 to Improve Transport Layer Security
Photon OS includes GnuTLS to help secure the transport layer. GnuTLS is a library that implements the SSL and TLS protocols to secure communications.
On Photon OS, SSL 3.0, which contains a known vulnerability, is disabled by default.
However, TLS 1.0, which also contains known vulnerabilities, is enabled by default.
To turn off TLS 1.0, perform the following steps:
- Create a directory named
/etc/gnutlscreate a file named
- In the
default-prioritiesfile, specify GnuTLS priority strings that remove TLS 1.0 and SSL 3.0 but retain TLS 1.1 and TLS 1.2.
- After adding a new
default-prioritiesfile or after modifying it, you must restart all applications, including SSH, with an open TLS session for the changes to take effect.
The following is an example of a
default-priorities file that contains GnuTLS priorities to disable TLS 1.0 and SSL 3.0:
console cat /etc/gnutls/default-priorities SYSTEM=NONE:!VERS-SSL3.0:!VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2:+AES-128-CBC:+RSA:+SHA1:+COMP-NULL
In this example, the priority string imposes system-specific policies. The
NONE keyword means that no algorithms, protocols, or compression methods are enabled, so that you can enable specific versions individually later in the string. The priority string then specifies that SSL version 3.0 and TLS version 1.0 be removed, as marked by the exclamation point. The priority string then enables, as marked by the plus sign, versions 1.1 and 1.2 of TLS. The cypher is AES-128-CBC. The key exchange is RSA. The MAC is SHA1. And the compression algorithm is COMP-NULL.
On Photon OS, you can verify the system-specific policies in the
default-priorities file as follows:
- Concatenate the
default-prioritiesfile to check its contents:
root@photon-rc [ ~ ]# cat /etc/gnutls/default-priorities SYSTEM=NONE:!VERS-SSL3.0:!VERS-TLS1.0:+VERS-TLS1.1:+VERS-TLS1.2:+AES-128-CBC:+RSA:+SHA1:+COMP-NULL
- Run the following command to check the protocols that are enabled for the system:
root@photon-rc [ /etc/gnutls ]# gnutls-cli --priority @SYSTEM -l Cipher suites for @SYSTEM TLS_RSA_AES_128_CBC_SHA1 0x00, 0x2f SSL3.0 Certificate types: none Protocols: VERS-TLS1.1, VERS-TLS1.2 Compression: COMP-NULL Elliptic curves: none PK-signatures: none
For information about the GnuTLS priority strings, see https://gnutls.org/manual/html_node/Priority-Strings.html.
For information about the vulnerability in SSL 3.0, see SSL 3.0 Protocol Vulnerability and POODLE Attack.
For information about the vulnerabilities in TLS 1.0, see Guidelines for the Selection, Configuration, and Use of Transport Layer Security (TLS) Implementations.