Ubuntu: Security Advisory (USN-7497-1)

The remote host is missing an update for the SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a referenced sources, and are Copyright C by the respective right holders. SPDX-License-Identifier: GPL-2.0-only ifdescription...

Ensure That Rotation Is Enabled for Audit Logs

maxlogfileaction decides the action taken when the size of a log file reaches the upper limit. By default, ROTATE is configured in openEuler, indicating that a new log file is created when the size of a log file reaches the upper limit and the original log file is not deleted. numlogs specifies t...

Correctly Configure the Default File Permission For rsyslog

Log files record system behaviors. The rsyslog log tool records logs in specified files. When the specified log file does not exist in the system, rsyslog creates a log file. The permission of the created log file can be configured in the rsyslog configuration file. The configuration of the defau...

Do Not Allow Empty Links

Empty links are redundant files and waste system resources. In addition, if a file is installed or created at the target location of an empty link, the file can be accessed through the link, leading to possible information leakage or tampering. If the file to which the link points has been delete...

Ensure That Passwords Do Not Contain User Names

To ensure user security, you must configure passwords that do not contain user names. If a password is the same as the user name or the user name in reverse order, or contains the user name, attackers can guess the password easily. This requirement is not exerted on passwords of users whose names...

Enable Kernel ASLR

Address-space layout randomization ASLR randomly arranges the positions of the stack, function libraries, and programs to slightly different positions each time. As a result, the correct positions cannot be guessed, and buffer overflow attacks fail. In the Linux kernel, ASLR is classified into...

Ensure Kernel SMEP is Enabled

Supervisor Mode Execution Prevention SMEP can be enabled to prevent the user-space code execution on the kernel. If SMEP is not enabled, attackers can execute the user-space code through kernel-mode code redirection, which increases the attack surface and reduces system security. SMEP is enabled ...

Do Not Enable Login Capabilities for Users Who Are Not Meant for Direct Login

Typically, a Linux system has multiple users, not all of which are used for login. For instance, some users are automatically created during the installation of software packages like systemd and dhcp. These users serve specific purposes, such as running related software services. It is essential...

Configure Audit Rules for SELinux

SELinux is a mandatory access control function component of Linux. It is used to implement fine-grained permission control on processes and files. You are advised to audit configurations of SELinux configuration files and policy files and record modification logs. If SELinux audit is not...

Configure Proper Key Algorithms for User Authentication

If the public and private key authentication mode is used, the public and private key algorithms on the client must be restricted to avoid using insecure algorithms that have been phased out in the industry. The recommended security algorithms are sorted by priority as follows. The algorithms hav...

Ensure That the Log Size Limit Is Correct

The size of an audit log file must be limited. The log rotation mechanism can be used to create new log files once the file size limit is reached. If the upper limit is too high, the size of a single log file may be too large, which is inconvenient for management. If the upper limit is too low, t...

Do Not Install the X Window System

X Window System X for short provides a GUI for users to log in and perform operations in Linux. Generally, servers do not require a GUI. Administrators can configure and modify a server through the CLI. X SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a...

Do Not Install the rsync Service

The rsync service can synchronize data between servers or between local drive partitions. However, information leakage risks exist because rsync uses non-encrypted transmission protocols. If the rsync service is enabled and data is transmitted between servers over the network, attackers can...

Ensure That the Unnecessary SUID/SGID Bit on a File Is Deleted

SUID set user ID and SGID set group ID are special permission bits used to control program permissions in UNIX and UNIX-like OSs, including Linux. It is important to ensure that files do not contain unnecessary SUID or SGID bits to improve system security. These bits allow files to run with the...

Record the cron Logs

Generally, cron is used to schedule tasks in Linux. Because cron can be exploited by hackers to load malicious code, all the cron logs need to be recorded to trace system exceptions. Otherwise, the exception information cannot be displayed in logs when there are malicious operations. As a result,...

Disable tcp_timestamps

tcptimestamps is used to record the time when TCP data packets are sent. It can be used for RTT measurement RTTM and protection against wrapped sequence number PAWS. It is a bidirectional option and takes effect only when it is enabled on both the client and server. If this option is enabled, the...

Ensure That the UIDs Are Unique

The UIDs of users in /etc/passwd must be unique. In the Linux system, user permissions are determined based on UIDs. If multiple users use the same UID, these users have the same permissions and users of the users can access each other SPDX-FileCopyrightText: 2025 Greenbone AG Some text...

Ensure That the Permissions on Important Files and Directories Are Minimized

According to the principle of least privilege, the minimum access permission must be correctly set for key files or directories in the system, especially those containing sensitive information. Only users with relevant permissions can access these files or directories. If the file or directory...

Configure the Authentication Blocklist and Allowlist Properly

SSH provides the blocklist and allowlist function. You can set a list of users or user groups to allow or deny SSH login for them. By default, this function is not configured in openEuler. The related fields are as follows: AllowUsers userlist specifies the space-separated users who are allowed t...

Ensure That the Drive Space Threshold Is Correct

If the drive space is fully occupied by auditd logs, services may fail to be executed. Therefore, set related configuration items in advance to prevent serious system issues caused by low drive space. The following items in the /etc/audit/auditd.conf file have been configured with default values ...

Ubuntu: Security Advisory (USN-7492-1)

The remote host is missing an update for the SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a referenced sources, and are Copyright C by the respective right holders. SPDX-License-Identifier: GPL-2.0-only ifdescription...

Disable IP Forwarding

If a node does not function as a gateway server, disable the IP forwarding function. Otherwise, attackers can use the node as a router. In the container scenario, if network packets need to be forwarded through the host, IP forwarding is allowed. SPDX-FileCopyrightText: 2025 Greenbone AG Some tex...

Configure Proper Policies for OUTPUT of nftables

There are two occasions in which a server sends outgoing packets: 1. The local host process proactively connects to an external server, for example, performing an HTTP access, or sending data to a log server. 2. The local host responds to the external access to the local services. If no policy is...

Configure the nftables Policies for Loopback Properly

The loopback address 127.0.0.0/8 is a special address on a server. It is irrelevant to NICs and is mainly used for the inter-process communication of a local device. Packets with the source address 127.0.0.0/8 from NICs should be discarded. If policies related to the loopback address are improper...

Drive Data Should Be Managed in Partitions

When installing the OS, plan different partitions for OS data and service data based on the scenario. Do not store all data in the same drive or partition. Properly planning drive partitions avoids or reduces the following risks: 1. Log files are too large and use up the space of the service driv...

Configure Proper SSH Key Exchange Algorithms

Key exchange is a process in which two parties exchange keys to allow the use of an encryption algorithm. A secure key exchange algorithm enables them to securely exchange keys, thereby using encryption algorithms to encrypt messages to be sent and decrypt received messages. Set the SSH key...

Disable PermitUserEnvironment

PermitUserEnvironment allows users to set SSH environment variables, which may be exploited by attackers to launch attacks. If PermitUserEnvironment is set to yes, attackers can modify SSH environment variables to evade the security mechanism or execute attack code. This configuration must be...

Configure Proper Policies for OUTPUT of iptables

There are two occasions in which a server sends outgoing packets: 1. The local host process proactively connects to an external server, for example, performing an HTTP access, or sending data to a log server. 2. The local host responds to the external access to the local services. If no policy is...

Do Not Install the LDAP Client

Lightweight Directory Access Protocol LDAP is a protocol that provides access control and is used to maintain distributed directory information. Running the LDAP service requires additional system resources and expands the attack surface. Therefore, do not install the LDAP client in the service...

Enable AIDE

Advanced intrusion detection environment AIDE is an intrusion detection tool that checks the integrity of system files and directories and identifies those maliciously tampered with. In principle, the integrity check can be performed only after an AIDE benchmark database is constructed, which...

Configure Audit Rules for Privilege Escalation Operations

In openEuler, logs of privilege escalation operations using the sudo command are recorded in the /var/log/secure file by default. This file also records other authentication-related security logs. If you want to audit privilege escalation operations using sudo, you are advised to record logs...

Enable the haveged Service

The haveged service can generate an unpredictable stream of random numbers in a simple way. These random numbers can fill the system entropy pool, which can solve the problem of low system entropy in some cases. You are advised to enable this service to meet the needs of encryption, decryption, o...

Bind Network Interfaces to the Correct Zones

Different filtering policies can be configured for different firewall zones. If the server network is complex and has multiple interfaces that provide different service functions, it is recommended that interfaces be configured in different zones and different firewall policies be configured. For...

Do Not Install the HTTP Service

HyperText Transfer Protocol HTTP is a simple request-response protocol and usually runs over TCP. It specifies what messages the client may send to the server and what responses the client receives. Request and response messages include headers in ASCII, and the message content often uses a...

Configure Proper Association Policies for INPUT and OUTPUT of nftables

Although you can configure protocols, IP addresses, and port numbers to add policies for packets entering and leaving a server to the INPUT and OUTPUT chains, it is difficult to configure suitable policies using the sport parameter due to complicated situations. For example, a client accesses the...

Enable auditd to Start upon System Startup

By enabling auditd to start upon system startup, you can audit the events generated during system startup before the auditd service is started. If audit is not enabled during system startup, you may not be able to audit attacks during the startup procedure. By default, audit is not enabled during...

Do Not Enable the LDAP Service

Lightweight Directory Access Protocol LDAP is a protocol that provides access control and is used to maintain distributed directory information. The LDAP service increases system resource usage and expands the attack surface. If the LDAP service is not required, do not install the LDAP service. T...

Configure the Scripts Executed by crontab to Be Writable Only by Their Owners

crontab is the configuration file used by the system to execute scheduled tasks. The path of the configuration file is /etc/crontab. With crontab, the OS automatically executes the tasks defined by the administrator based on service requirements. Therefore, the execution scripts or programs...

Configure the chronyd Service Properly

If the time server is incorrectly configured, the time of the local server may be inconsistent with that of other servers or the standard time. If time is incorrect, services that strongly depend on time synchronization, such as market transactions, may be interrupted, and attackers may exploit t...

Configure the Rotate Policy in rsyslog

rsyslog collects logs from the system and records them in files. logrotate copies and compresses log files periodically and quantitatively to ensure that log files do not occupy too many drive resources or even cannot be maintained. If the rotate policy is not configured for log files, they will...

Ensure That the Password Complexity Is Set Correctly

Simple passwords, including short passwords and passwords containing only digits or letters, are easy to guess by brute force cracking tools. As such, users are required to set complex passwords. For service scenarios with high security requirements, follow industry best practices. For example,...

Ensure That a User Is Locked After a Specified Number of Login Failures

If a user fails to log in to the system for a specified number of consecutive times, the system locks the user. That is, the user is not allowed to log in to the system for a specified period of time to prevent malicious system password cracking. During the lockout period, any input is considered...

Configure the Core Dump Properly

A core dump records the memory status when a program stops abnormally or breaks down. It helps locate faults but may contain sensitive information in the process memory. In some cases, the core dump function needs to be enabled to record problem causes. When enabling the core dump function,...

Ensure That Passwords Are Encrypted Using Strong Hash Algorithms

For system security, passwords cannot be stored in plaintext in the system and must be encrypted. Irreversible cryptographic algorithms must be used in scenarios where passwords do not need to be recovered. If a password is encrypted with a weak algorithm, attackers can increase the computing pow...

Configure the Remote Log Server

rsyslog can send local logs to a remote log server for unified storage. This facilitates centralized log management, prevents local logs from occupying too much drive space and being tampered with. If remote log storage is not configured, rsyslog logs are stored in local files. As far as the...

Ensure That Scripts Writable by Low-Privilege Users Cannot Be Configured in the sudoers Configuration File

The sudo command enables a specified common user to execute certain programs with the root permission. The corresponding configuration file is /etc/sudoers. The administrator can configure rules to enable some scripts or binary files to run with the root permission. Therefore, only the root user...

Start the cron Daemon Properly

The cron daemon is used to execute batch processing jobs on the system. Even if the OS does not have user jobs that need to be run, some system jobs need to be run, including important jobs such as security monitoring. The cron daemon is used to execute these jobs. If the cron daemon is not start...

Do Not Install the LDAP Service

Lightweight Directory Access Protocol LDAP is a protocol that provides access control and is used to maintain distributed directory information. The LDAP service increases system resource usage and expands the attack surface. If the LDAP service is not required, do not install the LDAP service. T...

Do Not Preset authorized_keys for the SSH Service

authorizedkeys specifies the public key of the remote host. You can store the public key in the $HOME/.ssh/authorizedkeys file in the home directory for public key authentication. Then you can directly log in to the system. If authorizedkeys is preset in the system and public and private key...

Configure the Default Policies of iptables to DROP Properly

Generally, iptables policies can be configured in allowlist or blocklist mode. You are advised to configure iptables policies in allowlist mode. Connections that do not comply with the rules in the allowlist are prohibited. Therefore, you can configure the DROP or REJECT policy for the INPUT,...