APACHE 2.2 Server for Windows Security Technical Implementation Guide

Normally, a service account is established for the web server. This is because a privileged account is not desirable and the server is designed to run for long uninterrupted periods of time. The SA or Web Manager will need password access to the web server to restart the service in the event of an emergency as the web server is not to restart automatically after an unscheduled interruption. If the password is not entrusted to an SA or web manager the ability to ensure the availability of the web server is compromised.System AdministratorInformation Assurance OfficerWeb Administrator

It is important to segregate public web server resources from private resources located behind the DoD DMZ in order to protect private assets. When folders, drives or other resources are directly shared between the public web server and private servers the intent of data and resource segregation can be compromised.Web Administrator

Normally, a service account is established for the web service to run under rather than permitting it to run as part of the local system. The password on such accounts must be changed at least annually. If the password is not changed periodically, the potential for a malicious party to gain access to the web services account is greatly enhanced.Web Administrator

The presence of a compiler on a production server facilitates the malicious user’s task of creating custom versions of programs and installing Trojan Horses or viruses. For example, the attacker’s code can be uploaded and compiled on the server under attack.Web Administrator

To minimize exposure of private assets to unnecessary risk by attackers, public web servers must be isolated from internal systems. Public web servers are by nature more vulnerable to attack from publically based sources, such as the public Internet. Once compromised, a public web server might be used as a base for further attack on private resources, unless additional layers of protection are implemented. Public web servers must be located in a DoD DMZ Extension, if hosted on the NIPRNet, with carefully controlled access. Failure to isolate resources in this way increase risk that private assets are exposed to attacks from public sources.System Administrator

Private web servers, which host sites that serve controlled access data, must be protected from outside threats in addition to insider threats. Insider threat may be accidental or intentional but, in either case, can cause a disruption in service of the web server. To protect the private web server from these threats, it must be located on a separate controlled access subnet and must not be a part of the public DMZ that houses the public web servers. It also cannot be located inside the enclave as part of the local general population LAN.System Administrator

All automated information systems are at risk of data loss due to disaster or compromise. Failure to provide adequate protection to the administration tools creates risk of potential theft or damage that may ultimately compromise the mission. Adequate protection ensures that server administration operates with less risk of losses or operations outages. The key web service administrative and configuration tools must be accessible only by the authorized web server administrators. All users granted this authority must be documented and approved by the ISSO. Access to the IIS Manager will be limited to authorized users and administrators.Web Administrator

In addition to OS restrictions, access rights to files and directories can be set on a web site using the web server software. That is, in addition to allowing or denying all access rights, a rule can be specified that allows or denies partial access rights. For example, users can be given read-only access rights to files, to view the information but not change the files. This check verifies that the htpasswd file is only accessible by system administrators or web managers, with the account running the web service having group permissions of read and execute. Htpasswd is a utility used by Netscape and Apache to provide for password access to designated web sites. IWeb Administrator

This check verifies that the key web server system configuration files are owned by the SA or Web Manager controlled account. These same files which control the configuration of the web server, and thus its behavior, must also be accessible by the account which runs the web service. If these files are altered by a malicious user, the web server would no longer be under the control of its managers and owners; properties in the web server configuration could be altered to compromise the entire server platform. System AdministratorWeb Administrator

This check verifies that the key web server system configuration files are owned by the SA or Web Manager controlled account. These same files which control the configuration of the web server, and thus its behavior, must also be accessible by the account which runs the web service. If these files are altered by a malicious user, the web server would no longer be under the control of its managers and owners; properties in the web server configuration could be altered to compromise the entire server platform.Web Administrator

Incoming E-mail has been known to provide hackers with access to servers. Disabling the incoming mail service prevents this type of attacks. Additionally, Email represents the main use of the Internet. It is specialized application that requires the dedication of server resources. To combine this type of transaction processing function with the file serving role of the web server creates an inherent conflict. Supporting mail services on a web server opens the server to the risk of abuse as an email relay. This check verifies, by checking the OS, that incoming e-mail is not supported.Web Administrator

Windows Scripting Host (WSH) is installed under either a Typical or Custom installation option of a Microsoft Network Server. This technology permits the execution of powerful script files from the Windows NT command line. This technology is also classified as a Category I Mobile Code. If the access to these files is not tightly controlled, a malicious user could readily compromise the server by using a form to send input to these scripting engines.System Administrator

By their very nature, CGI type files permit the anonymous web user to interact with data and perhaps store data on the web server. In many cases, CGI scripts exercise system-level control over the server’s resources. These files make appealing targets for the malicious user. If these files can be modified or exploited, the web server can be compromised. These files must be monitored by a security tool that reports unauthorized changes to these files.System Administrator

The web server installation and configuration plan should not support the co-hosting of multiple services such as Domain Name Service (DNS), e-mail, databases, search engines, indexing, or streaming media on the same server that is providing the web publishing service. By separating these services additional defensive layers are established between the web service and the applicable application should either be compromised. Disallowed or restricted services in the context of this vulnerability applies to services that are not directly associated with the delivery of web content. An operating system that supports a web server will not provide other services (e.g., domain controller, e-mail server, database server, etc.). Only those services necessary to support the web server and its hosted sites are specifically allowed and may include, but are not limited to, operating system, logging, anti-virus, host intrusion detection, administrative maintenance, or network requirements.System Administrator

The IAVM process does not address all patches that have been identified for the host operating system or, in this case, the web server software environment. Many vendors have subscription services available to notify users of known security threats. The site needs to be aware of these fixes and make determinations based on local policy and what software features are installed, if these patches need to be applied. In some cases, patches also apply to middleware and database systems. Maintaining the security of web servers requires frequent reviews of security notices. Many security notices mandate the installation of a software patch to overcome security vulnerabilities. SAs and ISSOs should regularly check the vendor support web site for patches and information related to the web server software. All applicable security patches will be applied to the operating system and to the web server software. Security patches are deemed applicable if the product is installed, even if it is not used or is disabled.Information Assurance Officer

Running the web server with excessive privileges presents an increased risk to the web server. In the event the web server’s services are compromised, the context by which the web server is running will determine the amount of damage that may be caused by the attacker. If the web server is run as an administrator or as an equivalent account, the attacker will gain administrative access through the web server. If, on the other hand, the web server is running with least privilege required to function, the capabilities of the attacker will be greatly decreased.System Administrator

A PKI certificate is a digital identifier that establishes the identity of an individual or a platform. A server that has a certificate provides users with third-party confirmation of authenticity. Most web browsers perform server authentication automatically; the user is notified only if the authentication fails. The authentication process between the server and the client is performed using the SSL/TLS protocol. Digital certificates are authenticated, issued, and managed by a trusted Certification Authority (CA). The use of a trusted certificate validation hierarchy is crucial to the ability to control access to your server and prevent unauthorized access. This hierarchy needs to lead to the DoD PKI Root CA or to an approved External Certificate Authority (ECA) or are required for the server to function.Information Assurance Officer

Without the use of a certificate validation process, the site is vulnerable to accepting certificates that have expired or have been revoked. This would allow unauthorized individuals access to the web server. This also defeats the purpose of the multi-factor authentication provided by the PKI process.System Administrator

Remote web authors should not be able to upload files to the DocumentRoot directory structure without virus checking and checking for malicious or mobile code. A remote web user whose agency has a Memorandum of Agreement (MOA) with the hosting agency and has submitted a DoD form 2875 (System Authorization Access Request (SAAR)) or an equivalent document will be allowed to post files to a temporary location on the server. All posted files to this temporary location will be scanned for viruses and content checked for malicious or mobile code. Only files free of viruses and malicious or mobile code will be posted to the appropriate Document Root directory.Web AdministratorSystem Administrator

These Timeout requirements are set to mitigate the effects of several types of denial of service attacks. Although there is some latitude concerning the settings themselves, the requirements attempt to provide reasonable limits for the protection of the web server. If necessary, these limits can be adjusted to accommodate the operational requirement of a given system.Web Administrator

The KeepAlive extension to HTTP/1.0 and the persistent connection feature of HTTP/1.1 provide long lived HTTP sessions which allow multiple requests to be sent over the same connection. These requirements are set to mitigate the effects of several types of denial of service attacks. Although there is some latitude concerning the settings themselves, the requirements attempt to provide reasonable limits for the protection of the web server. If necessary, these limits can be adjusted to accommodate the operational requirement of a given system.Web Administrator

The number of seconds Apache will wait for a subsequent request before closing the connection. Once a request has been received, the timeout value specified by the Timeout directive applies. Setting KeepAliveTimeout to a high value may cause performance problems in heavily loaded servers. The higher the timeout, the more server processes will be kept occupied waiting on connections with idle clients. These requirements are set to mitigate the effects of several types of denial of service attacks.Web Administrator

CGI scripts are one of the most exploited vulnerabilities on web servers. CGI script execution in Apache can be accomplished via two methods. The first method uses the ScriptAlias directive to tell the server everything in that directory is a CGI script. The second method uses a combination of the Options directive and AddHandler or SetHandler directives. For situations where the combination of the Options directive and Handler directives are used, the ability to centrally manage scripts is lost, creating vulnerability on the web server. It is best to manage scripts using the ScriptAlias directive.Web Administrator

The Options directive configures the web server features that are available in particular directories. The FollowSymLinks option controls the ability of the server to follow symbolic links. A symbolic link allows a file or a directory to be referenced using a symbolic name raising a potential hazard if symbolic linkage is made to a sensitive area. When web scripts are executed and symbolic links are allowed, the web user could be allowed to access locations on the web server that are outside the scope of the web document root or home directory.Web Administrator

Apache HTTPD supports content negotiation as described in the HTTP/1.1 specification. It can choose the best representation of a resource based on the browser-supplied preferences for media type, languages, character set and encoding. It also implements a couple of features to give more intelligent handling of requests from browsers that send incomplete negotiation information. Content negotiation, or more accurately content selection, is the selection of the document that best matches the clients capabilities, from one of several available documents. There are two implementations of this. • A type map (a file with the handler type-map) which explicitly lists the files containing the variants. • A Multiviews search (enabled by the Multiviews Options), where the server does an implicit filename pattern match, and choose from amongst the results. A MultiViews search is where the server does an implicit filename pattern match, and chooses from the results. For example, if you have a file called configuration.php (or other extension) in root folder and you set up a rule in your htaccess for a virtual folder called configuration/ then you'll have a problem with your rule because the server will choose configuration.php automatically if MultiViews is enabled. An attacker can use the MultiViews functionality to aid in finding hidden file processes on the directory and potentially gather further sensitive information. MultiViews is a per-directory option, meaning it can be set, or explicitly disabled, with an Options directive within a , or section in httpd.conf, or (if AllowOverride is properly set) in .htaccess files. To explicitly disable an Options functionality, the option must be listed on every uncommented Options directive with a preceding the option. The "-" preceding the option configures Apache to explicitly disable the option. An Options directive with "none" will also disable the functionality. If the option is listed on an Options directive line without a preceding - or without anything preceding it or with a "+" preceding it or not configured at all, the MultiViews option is enabled and is vulnerable. Web Administrator

Directory options directives are directives that can be applied to further restrict access to file and directories. If a URL which maps to a directory is requested, and there is no DirectoryIndex (e.g., index.html) in that directory, then mod_autoindex will return a formatted listing of the directory. The Indexes option allows for the functionality of presenting a formatted listing of the directory. Returning a formatted listing of the directory represents a vulnerability since it will allow an attacker to have knowledge of the directory contents and potentially gather sensitive information. To explicitly disable an Options functionality, the option must be listed on every uncommented Options directive with a preceding the option. The "-" preceding the option configures Apache to explicitly disable the option. An Options directive with "none" will also disable the functionality. If the option is listed on an Options directive line without a preceding - or without anything preceding it or with a "+" preceding it or not configured at all, the Indexes option is enabled and is vulnerable. Web Administrator

Buffer overflow attacks are carried out by a malicious attacker sending amounts of data that the web server cannot store in a given size buffer. The eventual overflow of this buffer can overwrite system memory. Subsequently an attacker may be able to elevate privileges and take control of the server. The Apache directives listed below limit the size of the various HTTP header sizes thereby limiting the chances for a buffer overflow. The LimitRequestBody directive allows the user to set a limit on the allowed size of an HTTP request message body within the context in which the directive is given (server, per-directory, per-file or per-location). If the client request exceeds that limit, the server will return an error response instead of servicing the request. The size of a normal request message body will vary greatly depending on the nature of the resource and the methods allowed on that resource. CGI scripts typically use the message body for retrieving form information. Implementations of the PUT method will require a value at least as large as any representation that the server wishes to accept for that resource. This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.Web Administrator

Buffer overflow attacks are carried out by a malicious attacker sending amounts of data that the web server cannot store in a given size buffer. The eventual overflow of this buffer can overwrite system memory. Subsequently an attacker may be able to elevate privileges and take control of the server. This Apache directive limits the size of the various HTTP header sizes, thereby limiting the chances for a buffer overflow. The LimitRequestFields directive allows the server administrator to modify the limit on the number of request header fields allowed in an HTTP request. A server needs this value to be larger than the number of fields that a normal client request might include. The number of request header fields used by a client rarely exceeds 20, but this may vary among different client implementations, often depending upon the extent to which a user has configured their browser to support detailed content negotiation. Optional HTTP extensions are often expressed using request header fields. This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks. The value should be increased if normal clients see an error response from the server that indicates too many fields were sent in the request.Web Administrator

Buffer overflow attacks are carried out by a malicious attacker sending amounts of data that the web server cannot store in a given size buffer. The eventual overflow of this buffer can overwrite system memory. Subsequently an attacker may be able to elevate privileges and take control of the server. This Apache directive limits the size of the various HTTP header sizes, thereby limiting the chances for a buffer overflow. The LimitRequestFieldSize directive allows the server administrator to reduce or increase the limit on the allowed size of an HTTP request header field. A server needs this value to be large enough to hold any one header field from a normal client request. The size of a normal request header field will vary greatly among different client implementations, often depending upon the extent to which a user has configured their browser to support detailed content negotiation. SPNEGO authentication headers can be up to 12392 bytes. This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.Web Administrator

Buffer overflow attacks are carried out by a malicious attacker sending amounts of data that the web server cannot store in a given size buffer. The eventual overflow of this buffer can overwrite system memory. Subsequently an attacker may be able to elevate privileges and take control of the server. This Apache directive limits the size of the various HTTP header sizes, thereby limiting the chances for a buffer overflow. The LimitRequestLine directive allows the server administrator to reduce or increase the limit on the allowed size of a client's HTTP request-line. Since the request-line consists of the HTTP method, URI, and protocol version, the LimitRequestLine directive places a restriction on the length of a request-URI allowed for a request on the server. A server needs this value to be large enough to hold any of its resource names, including any information that might be passed in the query part of a GET request. This directive gives the server administrator greater control over abnormal client request behavior, which may be useful for avoiding some forms of denial-of-service attacks.Web Administrator

Modules are the source of Apache httpd servers core and dynamic capabilities. Thus not every module available is needed for operation. Most installations only need a small subset of the modules available. By minimizing the enabled modules to only those that are required, we reduce the number of doors and have therefore reduced the attack surface of the web site. Likewise having fewer modules means less software that could have vulnerabilities.Web Administrator

The Apache mod_dav and mod_dav_fs modules support WebDAV ('Web-based Distributed Authoring and Versioning') functionality for Apache. WebDAV is an extension to the HTTP protocol which allows clients to create, move, and delete files and resources on the web server. WebDAV is not widely used, and has serious security concerns as it may allow clients to modify unauthorized files on the web server. Therefore, the WebDav modules mod_dav and mod_dav_fs should be disabled.Web Administrator

The Apache mod_info module provides information on the server configuration via access to a /server-info URL location, while the mod_status module provides current server performance statistics. While having server configuration and status information available as a web page may be convenient, it is recommended that these modules not be enabled: Once mod_info is loaded into the server, its handler capability is available in per-directory .htaccess files and can leak sensitive information from the configuration directives of other Apache modules such as system paths, usernames/passwords, database names, etc. If mod_status is loaded into the server, its handler capability is available in all configuration files, including per-directory files (e.g., .htaccess) and may have security-related ramifications.Web Administrator

The Apache proxy modules allow the server to act as a proxy (either forward or reverse proxy) of http and other protocols with additional proxy modules loaded. If the Apache installation is not intended to proxy requests to or from another network then the proxy module should not be loaded. Proxy servers can act as an important security control when properly configured, however a secure proxy server is not within the scope of this STIG. A web server should be primarily a web server or a proxy server but not both, for the same reasons that other multi-use servers are not recommended. Scanning for web servers that will also proxy requests is a very common attack, as proxy servers are useful for anonymizing attacks on other servers, or possibly proxying requests into an otherwise protected network.Web Administrator

The UserDir directive must be disabled so that user home directories are not accessed via the web site with a tilde (~) preceding the username. The directive also sets the path name of the directory that will be accessed. The user directories should not be globally enabled since it allows anonymous access to anything users may want to share with other users on the network. Also consider that every time a new account is created on the system, there is potentially new content available via the web site.Web Administrator

The PidFile directive sets the path to the process ID file to which the server records the process ID of the server, which is useful for sending a signal to the server process or for checking on the health of the process. If the PidFile is placed in a writable directory, other accounts could create a denial of service attack and prevent the server from starting by creating a PID file with the same name.Web Administrator

The ScoreBoardFile directive sets a file path which the server will use for Inter-Process Communication (IPC) among the Apache processes. If the directive is specified, then Apache will use the configured file for the inter-process communication. Therefore if it is specified it needs to be located in a secure directory. If the ScoreBoard file is placed in openly writable directory, other accounts could create a denial of service attack and prevent the server from starting by creating a file with the same name, and or users could monitor and disrupt the communication between the processes by reading and writing to the file.Web Administrator

The Apache Directory directive allows for directory specific configuration of access controls and many other features and options. One important usage is to create a default deny policy that does not allow access to Operating System directories and files, except for those specifically allowed. This is done, with denying access to the OS root directory. One aspect of Apache, which is occasionally misunderstood, is the feature of default access. That is, unless you take steps to change it, if the server can find its way to a file through normal URL mapping rules, it can and will serve it to clients. Having a default deny is a predominate security principal, and then helps prevent the unintended access, and we do that in this case by denying access to the OS root directory. The Order directive is important as it provides for other Allow directives to override the default deny.Web Administrator

The Apache Options directive allows for specific configuration of options, including execution of CGI, following symbolic links, server side includes, and content negotiation. The Options directive for the root OS level is used to create a default minimal options policy that allows only the minimal options at the root directory level. Then for specific web sites or portions of the web site, options may be enabled as needed and appropriate. No options should be enabled and the value for the Options Directive should be None.Web Administrator

Use the Apache TraceEnable directive to disable the HTTP TRACE request method. Refer to the Apache documentation for more details http://httpd.apache.org/docs/2.2/mod/core.html#traceenable. The HTTP 1.1 protocol requires support for the TRACE request method which reflects the request back as a response and was intended for diagnostics purposes. The TRACE method is not needed and is easily subject to abuse and should be disabled.Web Administrator

The Apache Listen directive specifies the IP addresses and port numbers the Apache web server will listen for requests. Rather than be unrestricted to listen on all IP addresses available to the system, the specific IP address or addresses intended must be explicitly specified. Specifically a Listen directive with no IP address specified, or with an IP address of zero’s should not be used. Having multiple interfaces on web servers is fairly common, and without explicit Listen directives, the web server is likely to be listening on an inappropriate IP address / interface that was not intended for the web server. Single homed system with a single IP addressed are also required to have an explicit IP address in the Listen directive, in case additional interfaces are added to the system at a later date.Web Administrator

The ScriptAlias directive controls which directories the Apache server "sees" as containing scripts. If the directive uses a URL-path name that is different than the actual file system path, the potential exists to expose the script source code.Web Administrator

To identify the type of web servers and versions software installed it is common for attackers to scan for icons or special content specific to the server type and version. A simple request like http://example.com/icons/apache_pb2.png may tell the attacker that the server is Apache 2.2 as shown below. The many icons are used primary for auto indexing, which is recommended to be disabled.Web Administrator

The Apache OverRide directive allows for .htaccess files to be used to override much of the configuration, including authentication, handling of document types, auto generated indexes, access control, and options. When the server finds an .htaccess file (as specified by AccessFileName) it needs to know which directives declared in that file can override earlier access information. When this directive is set to None, then .htaccess files are completely ignored. In this case, the server will not even attempt to read .htaccess files in the file system. When this directive is set to All, then any directive which has the .htaccess Context is allowed in .htaccess files.Web Administrator

The HTTP 1.1 protocol supports several request methods which are rarely used and potentially high risk. For example, methods such as PUT and DELETE are rarely used and should be disabled in keeping with the primary security principal of minimize features and options. Also since the usage of these methods is typically to modify resources on the web server, they should be explicitly disallowed. For normal web server operation, you will typically need to allow only the GET, HEAD and POST request methods. This will allow for downloading of web pages and submitting information to web forms. The OPTIONS request method will also be allowed as it is used to request which HTTP request methods are allowed.Web Administrator

During the initial setup of a Transport Layer Security (TLS) connection to the web server, the client sends a list of supported cipher suites in order of preference. The web server will reply with the cipher suite it will use for communication from the client list. If an attacker can intercept the submission of cipher suites to the web server and place, as the preferred cipher suite, a weak export suite, the encryption used for the session becomes easy for the attacker to break, often within minutes to hours.Web Administrator