F5 BIG-IP TMOS ALG Security Technical Implementation Guide

The "Max In Progress Sessions Per Client IP" setting in an APM Access Profile is a security configuration that limits the number of simultaneous sessions that can be initiated from a single IP address. This is particularly helpful in preventing a session flood, where a hacker might attempt to overwhelm the system by initiating many sessions from a single source. By capping the number of sessions per IP, this setting can help maintain the system's stability and integrity while also providing a layer of protection against such potential attacks. False positives may result from this setting in networks where users are behind a shared proxy. Sites must conduct operational testing to determine if there are adverse operational impacts. View Log reports to identify recurring IP sources within the user community. Max In Progress Sessions per Client IP represents the maximum number of sessions that can be in progress for a client IP address. When setting this value, take into account whether users will come from a NAT-ed or proxied client address and, if so, increase the value accordingly.

Automated monitoring of remote access traffic allows organizations to detect cyberattacks and also ensure ongoing compliance with remote access policies by inspecting connection activities of remote access capabilities. Remote access methods include both unencrypted and encrypted traffic (e.g., web portals, web content filter, TLS, and webmail). With inbound TLS inspection, the traffic must be inspected prior to being allowed on the enclave's web servers hosting TLS or HTTPS applications. With outbound traffic inspection, traffic must be inspected prior to being forwarded to destinations outside of the enclave, such as external email traffic.

Data mining is the analysis of large quantities of data to discover patterns and is used in intelligence gathering. Failure to prevent attacks launched against organizational information from unauthorized data mining may result in the compromise of information. Injection attacks allow an attacker to inject code into a program or query or inject malware onto a computer to execute remote commands that can read or modify a database or change data on a website. Web applications frequently access databases to store, retrieve, and update information. An attacker can construct inputs that the database will execute. This is most commonly referred to as a code injection attack. This type of attack includes XPath and LDAP injections. Compliance requires the ALG to have the capability to prevent code injections. Examples include a Web Application Firewalls (WAFs) or database application gateways. Satisfies: SRG-NET-000318-ALG-000014, SRG-NET-000319-ALG-000015

Data mining is the analysis of large quantities of data to discover patterns and is used in intelligence gathering. Failure to prevent attacks launched against organizational information from unauthorized data mining may result in the compromise of information. Injection attacks allow an attacker to inject code into a program or query or inject malware onto a computer to execute remote commands that can read or modify a database or change data on a website. These attacks include buffer overrun, XML, JavaScript, and HTML injections. Compliance requires the ALG to have the capability to prevent code injections. Examples include a Web Application Firewalls (WAFs) or database application gateways. Satisfies: SRG-NET-000318-ALG-000151, SRG-NET-000319-ALG-000153

Data mining is the analysis of large quantities of data to discover patterns and is used in intelligence gathering. Failure to prevent attacks launched against organizational information from unauthorized data mining may result in the compromise of information. SQL injection attacks are the most prevalent attacks against web applications and databases. These attacks inject SQL commands that can read, modify, or compromise the meaning of the original SQL query. An attacker can spoof identity; expose, tamper, destroy, or make existing data unavailable; or gain unauthorized privileges on the database server. Compliance requires the ALG to have the capability to prevent SQL code injections. Examples include a Web Application Firewalls (WAFs) or database application gateways. Satisfies: SRG-NET-000318-ALG-000152, SRG-NET-000319-ALG-000020

Display of a standardized and approved use notification before granting access to the network ensures privacy and security notification verbiage used is consistent with applicable federal laws, Executive Orders, directives, policies, regulations, standards, and guidance. System use notifications are required only for access via logon interfaces with human users and are not required when such human interfaces do not exist. This requirement applies to network elements that have the concept of a user account and have the logon function residing on the network element. The banner must be formatted in accordance with DTM-08-060. Use the following verbiage for network elements that can accommodate banners of 1300 characters: "You are accessing a U.S. Government (USG) Information System (IS) that is provided for USG-authorized use only. By using this IS (which includes any device attached to this IS), you consent to the following conditions: -The USG routinely intercepts and monitors communications on this IS for purposes including, but not limited to, penetration testing, COMSEC monitoring, network operations and defense, personnel misconduct (PM), law enforcement (LE), and counterintelligence (CI) investigations. -At any time, the USG may inspect and seize data stored on this IS. -Communications using, or data stored on, this IS are not private, are subject to routine monitoring, interception, and search, and may be disclosed or used for any USG-authorized purpose. -This IS includes security measures (e.g., authentication and access controls) to protect USG interests--not for your personal benefit or privacy. -Notwithstanding the above, using this IS does not constitute consent to PM, LE or CI investigative searching or monitoring of the content of privileged communications, or work product, related to personal representation or services by attorneys, psychotherapists, or clergy, and their assistants. Such communications and work product are private and confidential. See User Agreement for details." Use the following verbiage for operating systems that have severe limitations on the number of characters that can be displayed in the banner: "I've read & consent to terms in IS user agreem't." This policy only applies to ALGs (e.g., identity management or authentication gateways) that provide user account services as part of the intermediary services. Satisfies: SRG-NET-000041-ALG-000022, SRG-NET-000042-ALG-000023, SRG-NET-000043-ALG-000024

Without generating audit records that log usage of objects by subjects and other objects, it would be difficult to establish, correlate, and investigate the events relating to an incident, or identify those responsible for one. The device logs internal users associated with denied outgoing communications traffic posing a threat to external information systems. Audit records can be generated from various components within the information system (e.g., module or policy filter). Security objects are data objects which are controlled by security policy and bound to security attributes. Satisfies: SRG-NET-000492-ALG-000027, SRG-NET-000494-ALG-000029, SRG-NET-000495-ALG-000030, SRG-NET-000496-ALG-000031, SRG-NET-000497-ALG-000032, SRG-NET-000498-ALG-000033, SRG-NET-000499-ALG-000034, SRG-NET-000500-ALG-000035, SRG-NET-000501-ALG-000036, SRG-NET-000502-ALG-000037, SRG-NET-000503-ALG-000038, SRG-NET-000505-ALG-000039, SRG-NET-000513-ALG-000026, SRG-NET-000074-ALG-000043, SRG-NET-000075-ALG-000044, SRG-NET-000076-ALG-000045, SRG-NET-000077-ALG-000046, SRG-NET-000078-ALG-000047, SRG-NET-000079-ALG-000048, SRG-NET-000249-ALG-000146, SRG-NET-000383-ALG-000135, SRG-NET-000385-ALG-000138, SRG-NET-000392-ALG-000141, SRG-NET-000392-ALG-000142, SRG-NET-000392-ALG-000143, SRG-NET-000392-ALG-000147, SRG-NET-000392-ALG-000148, SRG-NET-000392-ALG-000149, SRG-NET-000370-ALG-000125

Application protocol anomaly detection examines application layer protocols such as SMTP to identify attacks based on observed deviations in the normal RFC behavior of a protocol or service. This type of monitoring allows for the detection of known and unknown exploits which exploit weaknesses of commonly used protocols. Since protocol anomaly analysis examines the application payload for patterns or anomalies, an SMTP proxy must be included in the ALG. This ALG will be configured to inspect inbound and outbound SMTP and extended SMTP communications traffic to detect protocol anomalies such as malformed message and command insertion attacks.

Application protocol anomaly detection examines application layer protocols such as FTP to identify attacks based on observed deviations in the normal RFC behavior of a protocol or service. This type of monitoring allows for the detection of known and unknown exploits which exploit weaknesses of commonly used protocols. Since protocol anomaly analysis examines the application payload for patterns or anomalies, an FTP proxy must be included in the ALG. This ALG will be configured to inspect inbound and outbound FTP communications traffic to detect protocol anomalies such as malformed message and command insertion attacks.

Application protocol anomaly detection examines application layer protocols such as HTTP to identify attacks based on observed deviations in the normal RFC behavior of a protocol or service. This type of monitoring allows for the detection of known and unknown exploits which exploit weaknesses of commonly used protocols. Since protocol anomaly analysis examines the application payload for patterns or anomalies, an HTTP proxy must be included in the ALG. This ALG will be configured to inspect inbound and outbound HTTP communications traffic to detect protocol anomalies such as malformed message and command insertion attacks. All inbound and outbound traffic, including HTTPS, must be inspected. However, the intention of this policy is not to mandate HTTPS inspection by the ALG. Typically, HTTPS traffic is inspected either at the source, destination and/or is directed for inspection by organizationally-defined network termination point.

Without reauthentication, users may access resources or perform tasks for which they do not have authorization. In addition to the reauthentication requirements associated with session locks, organizations may require reauthentication of individuals and/or devices in other situations, including (but not limited to) the following circumstances: 1. When authenticators change; 2. When roles change; 3. When security categories of information systems change; 4. When the execution of privileged functions occurs; 5. After a fixed period of time; 6. Periodically. Within the DOD, the minimum circumstances requiring reauthentication are privilege escalation and role changes. This requirement only applies to components where this is specific to the function of the device or has the concept of user authentication (e.g., VPN or ALG capability). This does not apply to authentication for the purpose of configuring the device itself (i.e., device management).

Without configuring a local cache of revocation data, there is the potential to allow access to users who are no longer authorized (users with revoked certificates). The intent of this requirement is to require support for a secondary certificate validation method using a locally cached revocation data, such as Certificate Revocation List (CRL), in case access to OCSP (required by CCI-000185) is not available. Based on a risk assessment, an alternate mitigation is to configure the system to deny access when revocation data is unavailable. This requirement applies to ALGs that provide user authentication intermediary services (e.g., authentication gateway or TLS gateway). This does not apply to authentication for the purpose of configuring the device itself (device management).

If the network does not provide safeguards against denial-of-service (DoS) attacks, network resources will be unavailable to users. Installation of content filtering gateways and application layer firewalls at key boundaries in the architecture mitigates the risk of DoS attacks. These attacks can be detected by matching observed communications traffic with patterns of known attacks and monitoring for anomalies in traffic volume/type. Detection components that use rate-based behavior analysis can detect attacks when signatures for the attack do not exist or are not installed. These attacks include zero-day attacks which are new attacks for which vendors have not yet developed signatures. Rate-based behavior analysis can detect sophisticated, distributed DoS (DDoS) attacks by correlating traffic information from multiple network segments or components. This requirement applies to the communications traffic functionality of the ALG as it pertains to handling communications traffic, rather than to the ALG device itself. Satisfies: SRG-NET-000362-ALG-000112, SRG-NET-000362-ALG-000126, SRG-NET-000192-ALG-000121

If the network does not provide safeguards against DoS attacks, network resources will be unavailable to users. Installation of content filtering gateways and application layer firewalls at key boundaries in the architecture mitigates the risk of DoS attacks. These attacks can be detected by matching observed communications traffic with patterns of known attacks. Detection components that use pattern recognition pre-processors can detect attacks when signatures for the attack do not exist or are not installed. These attacks include zero-day attacks which are new attacks for which vendors have not yet developed signatures. This requirement applies to the communications traffic functionality of the ALG as it pertains to handling communications traffic, rather than to the ALG device itself.

Invalid user input occurs when a user inserts data or characters into an application's data entry fields and the application is unprepared to process that data. This results in unanticipated application behavior potentially leading to an application or information system compromise. Invalid input is one of the primary methods employed when attempting to compromise an application. Network devices with the functionality to perform application layer inspection may be leveraged to validate data content of network communications. Checking the valid syntax and semantics of information system inputs (e.g., character set, length, numerical range, and acceptable values) verifies that inputs match specified definitions for format and content. Software typically follows well-defined protocols that use structured messages (i.e., commands or queries) to communicate between software modules or system components. Structured messages can contain raw or unstructured data interspersed with metadata or control information. If network elements use attacker-supplied inputs to construct structured messages without properly encoding such messages, then the attacker could insert malicious commands or special characters that can cause the data to be interpreted as control information or metadata. Consequently, the module or component that receives the tainted output will perform the wrong operations or otherwise interpret the data incorrectly. Pre-screening inputs prior to passing to interpreters prevents the content from being unintentionally interpreted as commands. Input validation helps to ensure accurate and correct inputs and prevent attacks such as cross-site scripting and a variety of injection attacks. This requirement applies to gateways and firewalls that perform content inspection or have higher-layer proxy functionality.

The malicious software detection functionality on network elements needs to be constantly updated to identify new threats as they are discovered. All malicious software detection functions must come with an update mechanism that automatically updates the application and any associated signature definitions. The organization (including any contractor to the organization) is required to promptly install security-relevant malicious code protection updates. Examples of relevant updates include antivirus signatures, detection heuristic rule sets, and/or file reputation data employed to identify and/or block malicious software from executing. Malicious code includes viruses, worms, Trojan horses, and spyware. This requirement is limited to ALGs, web content filters, and packet inspection firewalls that perform malicious code detection as part of their functionality.

Unauthorized or unapproved network services lack organizational verification or validation, and therefore may be unreliable or serve as malicious rogues for valid services. Examples of network services include service-oriented architectures (SOAs), cloud-based services (e.g., infrastructure as a service, platform as a service, or software as a service), cross-domain, Voice Over Internet Protocol, Instant Messaging, auto-execute, and file sharing. To comply with this requirement, the ALG may be configured to detect services either directly or indirectly (i.e., by detecting traffic associated with a service). This requirement applies to gateways/firewalls that perform content inspection or have higher-layer proxy functionality.

Unauthorized or unapproved network services lack organizational verification or validation, and therefore may be unreliable or serve as malicious rogues for valid services. Examples of network services include service-oriented architectures (SOAs), cloud-based services (e.g., infrastructure as a service, platform as a service, or software as a service), cross-domain, Voice Over Internet Protocol, instant messaging, auto-execute, and file sharing.

By requiring mutual authentication before any communication, it becomes significantly challenging for attackers to impersonate a client or server and exploit vulnerabilities. Furthermore, the encryption of all data transmitted between the client and server ensures that even if an attacker intercepts the data, it remains unintelligible without the correct keys. To ensure the use of the mTLS for session authentication, do not use the On-Demand Cert Auth VPE agent. Typically, when a client makes an HTTPS request, an SSL handshake request occurs at the start of an SSL session. However, if On-Demand is configured, the client SSL profile skips the initial SSL handshake, an On-Demand Cert Auth action can re-negotiate the SSL connection from an access policy by sending a certificate request to the user. This prompts a certificate screen to open. Setting ODCA to "require" the client cert means the client cannot get any farther in the APM VPE without providing a valid certificate. "Request" would ask the client for a certificate, but the client could still continue if they did not provide one. Thus, the Client Certificate must be set to "require" in the client SSL profile since just removing ODCA from the VPE alone will result in the client never getting prompted for a certificate. Within the Virtual Policy Editor (VPE) of the relevant Access Profile, do not use the On-Demand Cert Auth VPE agent. Configure only the Client Certification Inspection VPE Agent. This adjustment directs the BIG-IP to scrutinize the Client Certificate during the mTLS handshake process and extract the certificate's details into APM session variables.

This security measure helps limit the effects of denial-of-service attacks by employing antisession hijacking security safeguards. Session hijacking, also called cookie hijacking, is the exploitation of a valid computer session to gain unauthorized access to an application. The attacker steals (or hijacks) the cookies from a valid user and attempts to use them for authentication.

The Maximum Session Timeout setting configures a limit on the maximum amount of time a user's session is active without needing to reauthenticate. If the value is set to zero, the user's session is active until either the user terminates the session or the Inactivity Timeout value is reached (the default value is set to 604,800 seconds). When determining how long the maximum user session can last, it may be useful to review the access policy. For example, if the access policy requires that the user's antivirus signatures cannot be older than eight hours, the Maximum Session Timeout must not exceed that time limit. This is an APM Policy setting, which applies to APM authentication profiles for Virtual Servers and SSL VPN.

Without identifying and authenticating devices, unidentified or unknown devices may be introduced, thereby facilitating malicious activity.

Split tunneling would in effect allow unauthorized external connections, making the system more vulnerable to attack and to exfiltration of organizational information. A VPN hardware or software client with split tunneling enabled provides an unsecured backdoor to the enclave from the internet. With split tunneling enabled, a remote client has access to the internet while at the same time has established a secured path to the enclave via an IPsec tunnel. A remote client connected to the internet that has been compromised by an attacker on the internet, provides an attack base to the enclave’s private network via the IPsec tunnel. Hence, it is imperative that the VPN gateway enforces a no split-tunneling policy to all remote clients.

Remote access devices, such as those providing remote access to network devices and information systems, which lack automated, capabilities increase risk and makes remote user access management difficult at best. Remote access is access to DOD nonpublic information systems by an authorized user (or an information system) communicating through an external, non-organization-controlled network. Automated monitoring of remote access sessions allows organizations to detect cyberattacks and ensure ongoing compliance with remote access policies by auditing connection activities of remote access capabilities, from a variety of information system components (e.g., servers, workstations, notebook computers, smart phones, and tablets).

Allowing remote users to manually toggle a VPN connection can create critical security risks. With Always On VPN, if a secured connection to the gateway is lost, hybrid-working users will simply be disconnected from the internet until the issue is solved. "Always On" is a term that describes a VPN connection that is secure and always on after the initial connection is established. An Always On VPN deployment establishes a VPN connection with the client without the need for user interaction (e.g., user credentials). The remote client must not be able to access the Internet without first established a VPN session with a DOD site. Note that device compliance checks are still required prior to connecting to DOD resources. Although out of scope for this requirement, the connection process must ensure that remote devices meet security standards before accessing DOD resources. Devices that fail to meet compliance requirements can be denied access, reducing the risk of compromised endpoints.