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What Does Your User Agent Say About You?

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A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".

(Source: Mozilla.org)

User Agent String

Browser Data

User Agent Httpclient

author
David Lawrence
• Friday, 27 November, 2020
• 13 min read

Making statements based on opinion; back them up with references or personal experience. An intrinsic part of the modern web application is the ability to use external APIs and webpages.

(Source: www.cnblogs.com)

Contents

A common way to create HttpClient s in Web API and MVC projects for .NET is using a HttpClientFactory. This can be added to the Service Collection in Startup.cs and be Dependency Injected in each controller.

This helps you get an overview of the quality of your applications and to spot trends in your releases. We notify you when errors start happening using Slack, Microsoft Teams, mail or other forms of communication to help you react to errors before your users do.

The Chrome (or Chromium/Blink-based engines) user agent string is similar to Firefox’s. For compatibility, it adds strings like HTML, like Gecko and Safari.

The Opera browser is also based on the Blink engine, which is why it almost looks the same, but adds “Or/”. In this example, the user agent string is mobile Safari’s version.

Making statements based on opinion; back them up with references or personal experience. HTTP is the foundation of data communication for the World Wide Web.

user agents edge change agent firefox safari chrome googlebot crawlers adsense bots browsers engines etc such google
(Source: www.searchenginejournal.com)

The Re-sync() method sends a GET request to the specified URI as an asynchronous operation. It outputs the simple HTML code of the home page.

The GetStringAsync() sends a GET request to the specified URI and returns the response body as a string in an asynchronous operation. The HTTP POST method sends data to the server.

We turn an object into a JSON data with the help of the Newton soft. Json package. We send an asynchronous POST request with the Apostasy() method.

JSON (JavaScript Object Notation) is a lightweight data-interchange format. This format is easy for humans to read and write and for machines to parse and generate.

The official Internet media type for JSON is application/Jason. We transform the JSON response into a list of Contributor objects with the JsonConvert. DeserializeObject() method.

(Source: www.cnblogs.com)

The GetByteArrayAsync() sends a GET request to the specified URI and returns the response body as a byte array in an asynchronous operation. In HTTP protocol, basic access authentication is a method for an HTTP user agent (such as a web browser or a console application) to provide a username and password when making a request.

In basic HTTP authentication, a request contains a header field in the form of Authorization: Basic , where credentials am the base64 encoding of id and password joined by a single colon :. Note: The credentials are not encrypted; therefore, HTTP basic authentication must be used with the HTTPS protocol.

HTTP Basic authentication is the simplest technique for enforcing access controls to web resources. It does not require cookies, session identifiers, or login pages; rather, HTTP Basic authentication uses standard fields in the HTTP header.

Making statements based on opinion; back them up with references or personal experience. Ideally, this header would give servers the ability to perform content negotiation, sending down exactly those bits that best represent the requested resource in a given user agent, optimizing both bandwidth and user experience.

Brand and version information (e.g. “Chrome 69”) allows websites to work around known bugs in specific releases that aren’t otherwise detectable. For example, implementations of Content Security Policy have varied wildly between vendors, and it’s difficult to know what policy to send in an HTTP response without knowing what browser is responsible for its parsing and execution.

user agent firefox extension zone switchers restart needed bottom works simple line
(Source: www.extension.zone)

Developers will often negotiate what content to send based on the user agent and platform. Similarly to #1, OS revisions and architecture can be responsible for specific bugs which can be worked around in website’s code, and narrowly useful for things like selecting appropriate executables for download (32 vs 64 bit, ARM vs Intel, etc).

It introduces four new Client Hints () that can provide the client’s branding and version information, the underlying operating system’s branding and major version, as well as details about the underlying device. Rather than broadcasting this data to everyone, all the time, user agents can make reasonable decisions about how to respond to given sites' requests for more granular data, reducing the passive fingerprinting surface area exposed to the network.

The request header field gives a server information about the architecture of the platform on which a given user agent is executing. The request header field gives a server information about the device on which a given user agent is executing.

The request header field gives a server information about the platform on which a given user agent is executing. The request header field gives a server information about the platform version on which a given user agent is executing.

The request header field gives a server information about an useragent's branding and version. It is considered low entropy because it includes only the useragent's branding information, and the significant version number (both of which are fairly clearly sniffable by “examining the structure of other headers and by testing for the availability and semantics of the features introduced or modified between releases of a particular browser” ).

(Source: blog.csdn.net)

The request header field gives a server information about whether an user agent prefers a “mobile” user experience. It is considered low entropy because it is a single bit of information directly controllable by the user.

Collect pairs of brands and which represent the user agent, its equivalence class and/or its rendering engine. Append additional items to list containing objects, initialized with arbitrary and combinations.

Note: One approach to minimize caching variance when generating these random components could be to determine them at build time, and keep them identical throughout the lifetime of the user agent's significant version. Client Hints will not be delivered to non-secure endpoints (see the secure transport requirements in Section 2.2.1 of).

This means that user agent information will not be leaked over plaintext channels, reducing the opportunity for network attackers to build a profile of a given agent ’s behavior over time. The primary goal of Sergeant Client Hints is to reduce the default entropy available to the network for passive fingerprinting.

User agents ought to exercise judgement before granting access to this information, and MAY impose restrictions above and beyond the secure transport and delegation requirements noted above. For instance, user agents could choose to reveal only on requests it intends to download, giving the server the opportunity to serve the right binary.

agent internet firewall explorer client block using via attachment host
(Source: forums.untangle.com)

Resetting expectations may help to prevent abuse of the UA string’s brand in the short term, but probably won’t help in the long run. User agents brands containing more than a single entry could encourage standardized processing of the UA string.

By randomly including additional, intentionally incorrect, comma-separated entries with arbitrary ordering, they would reduce the chance that we ossify on a few required strings. In order to encourage sites to rely on equivalence classes based on Chromium versions rather than exact UA sniffing, Chrome might remove itself from the set entirely.

Browsers based on Chromium may use a similar UA string, but use their own brand as part of the set, enabling sites to count them. When adding arbitrary values to brands, user agents MUST make sure that receivers of the header adhere to Structured Header parsing, by adding escaped double-quotes, commas and semi-colons to those values.

The purpose of this is to make non-compliant server implementations immediately aware that their parsing code is inadequate. Note: One approach to minimize caching variance could be to determine the GREASE parts of the UA set at build time, and keep them identical throughout the lifetime of the useragent's significant version.

Restricting user -land JavaScript code from influencing and modifying UA-CH headers has various security related advantages. As such and based on discussions with the TAG, it seems reasonable to forbid write access to these headers from JavaScript (e.g. through fetch or Service Workers), and demarcate them as browser-controlled client hints, so they can be documented and included in requests without triggering CORS preflights.

user agent linux string strings
(Source: www.linux.org)

For example, if a user's product were called WikiBrowser, their user agent string might be WikiBrowser/1.0 Gecko/1.0. During the first browser war, many web servers were configured to send web pages that required advanced features, including frames, to clients that were identified as some version of Mozilla only.

Automated web crawling tools can use a simplified form, where an important field is contact information in case of problems. Automated agents are expected to follow rules in a special file called robots.txt “.

The popularity of various Web browser products has varied throughout the Web's history, and this has influenced the design of websites in such a way that websites are sometimes designed to work well only with particular browsers, rather than according to uniform standards by the World Wide Web Consortium (W3C) or the Internet Engineering Task Force (IETF). Websites often include code to detect browser version to adjust the page design sent according to the user agent string received.

Thus, various browsers have a feature to cloak or spoof their identification to force certain server-side content. For example, the Android browser identifies itself as Safari (among other things) in order to aid compatibility.

User agent sniffing is the practice of websites showing different or adjusted content when viewed with certain user agents. An example of this is Microsoft Exchange Server 2003's Outlook Web Access feature.

user agents spoofing
(Source: www.fastvue.co)

When viewed with Internet Explorer 6 or newer, more functionality is displayed compared to the same page in any other browsers. Web browsers created in the United States, such as Netscape Navigator and Internet Explorer, previously used the letters U, I, and N to specify the encryption strength in the user agent string.

Until 1996, when the United States government disallowed encryption with keys longer than 40 bits to be exported, vendors shipped various browser versions with different encryption strengths. Following the lifting of export restrictions, most vendors supported 256-bit encryption.

Browser Versions Carry 10.5 Bits of Identifying Information on Average “, Electronic Frontier Foundation, 27 January 2010. I've been rejected until I come back with Netscape” ^ “Android Browser Reports Itself as Apple Safari”.

^ User Agent String explained: Android WebKit Browser”. Mozilla/5.0 (Linux; U; Android 2.2; ends; HTC_DesireHD_A9191 Build/FRF91) Apple WebKit/533.1 (HTML, like Gecko) Version/4.0 Mobile Safari/533.1 ^ Emberton, Stephen.

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Sources
1 www.cisco.com - https://www.cisco.com/c/en/us/td/docs/security/firesight/user-agent/23/config-guide/Firepower-User-Agent-Configuration-Guide-v2-3/ConfigAgent.html
2 community.cisco.com - https://community.cisco.com/t5/network-security/sourcefire-user-agent/td-p/2934974
3 www.cisco.com - https://www.cisco.com/c/en/us/support/docs/security/firesight-management-center/118131-technote-sourcefire-00.html
4 www.cisco.com - https://www.cisco.com/c/en/us/td/docs/security/firesight/user-agent/25/config-guide/Firepower-User-Agent-Configuration-Guide-v2-5/ConfigAgent.html
5 community.cisco.com - https://community.cisco.com/t5/network-security/user-agent-on-windows-2016/td-p/3353699
6 www.webex.com - https://www.webex.com/downloads.html/