IEInternals

A look at Internet Explorer from the inside out. @EricLaw left Microsoft in 2012, but was named an IE MVP in '13 & an IE userAgent (http://useragents.ie) in '14

  • IEInternals

    Internet Explorer Cookie Internals (FAQ)

    • 67 Comments
    Over the five years I’ve worked on Internet Explorer, I’ve probably seen more questions from the community about HTTP cookies than on any other topic. Cookies are an integral component of most websites in use today, and hence problems or unexpected...
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    Bugs in IE8's Lookahead Downloader

    • 116 Comments
    All bugs mentioned in this post are now fixed . Internet Explorer has a number of features designed to render pages more quickly. One of these features is called the "Lookahead Downloader" and it's used to quickly scan the page as it comes in, looking...
  • IEInternals

    IE8's Native XMLHttpRequest Object Restrictions, Bugs, and Notes

    • 8 Comments
    Protocol Restriction Internet Explorer's native XMLHTTPRequest object permits requests to HTTP and HTTPS only; requests to FILE, FTP, or other URI schemes are blocked. Update : IE10 XHR supports CORS . Method Restriction The object permits only the...
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    Unshackling IE8 Performance

    • 37 Comments
    In general, IE8 is a significantly faster browser than prior versions. We made a number of major investments throughout the browser’s code to help ensure that IE users will have a great real-world experience on the web. However, it is definitely the...
  • IEInternals

    Internet Explorer's Cache-Control Extensions

    • 5 Comments
    Some time ago, I wrote a summary of how Internet Explorer’s cache works . At the time, I left out mention of the two cache-control directives introduced by IE5: pre-check and post-check . These directives enable a “background update”...
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    Protecting ActiveX Controls

    • 0 Comments
    When evaluating the security of Internet Explorer’s ActiveX support, there are two threats to consider: · Malicious controls · Malicious websites To mitigate the threat of malicious ActiveX controls (malware), features like the IE8 SmartScreen...
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    Retiring IE6...

    • 6 Comments
    Often, folks ask us why we continue to support IE6. The short answer is that because we've committed to doing so . But more importantly, even if we dropped support, most people who want to use IE6 would still use it anyway, just without the benefit of...
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    Notes on Proxy AutoConfiguration Scripts

    • 0 Comments
    I had someone ask me for help writing a Proxy AutoConfiguration script today. PAC files are basically simple JavaScript files that expose one function, FindProxyForURL(url, host) . The function returns a string containing a list of one or more proxies...
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    Q&A: Rendering Mode for Web Browser Controls (WebOCs)

    • 1 Comments
    Q: Eric, you mentioned that the IE8 Web Browser Control, hosted in Forms / WPF, runs in IE7 emulation mode by default. Is there a way to turn the emulation mode off and have the control work in "real" IE8 mode? A: Yes. This is controlled by a feature...
  • IEInternals

    IE and the Accept Header

    • 18 Comments
    RFC 2616 describes the Accept request header as follows: The Accept request-header field can be used to specify certain media types which are acceptable for the response. Accept headers can be used to indicate that the request is specifically limited...
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    The Privacy Impact of Add-ons: New APIs for IE8

    • 6 Comments
    By default, when starting a new session using IE8's InPrivate Browsing feature, toolbars and Browser Helper Objects are disabled. This is done to help protect the user's privacy: many toolbars and extensions maintain their own navigation/search/etc history...
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    Internet Explorer and Custom HTTP Headers

    • 0 Comments
    Someone recently asked me for a list of custom HTTP request and response headers introduced by the IE team over the years. Here's the list I've come up with so far (including a few that were introduced before I joined the team): Request Headers ...
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    Cool deal: Windows 7 Pre-orders half price for a limited time

    • 0 Comments
    Not exactly IE related, although IE8 is included in Windows 7: Until July 11th, Windows 7 upgrade pre-orders are available for half-price . Home Premium is $50, and Professional is $100. -Eric
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    Thoughts on Declaring Security Policies

    • 2 Comments
    My thoughts about Mozilla's Content Security Policy proposal were just published over on the IEBlog. I actually have quite a bit more to say (at even greater length :-) about declarative security mechanisms, and some more technical feedback specific to...
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    User Account Control in Windows 7

    • 0 Comments
    It isn't directly related to Internet Explorer, but Mark Russinovich's Inside Windows7 User Account Control article over on TechNet provides an illuminating explanation of why UAC isn't a security boundary, but why it helps protect against malware anyway...
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    Handling Mixed (HTTPS/HTTPS) Content

    • 128 Comments
    Update: IE9 includes improved handling of Mixed Content. Click to learn more... Background As we developed Internet Explorer 8, we spent quite a bit of time pondering what to do about IE7’s infamous “Mixed Content” warning prompt...
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    WebOCs, popups, and the default browser

    • 1 Comments
    Applications which host the WebOC (Web Browser control) may choose to support popups and new windows by hooking the NewWindow3 event and returning in ppDisp a pointer to a new, hidden, non-navigated WebBrowser object or InternetExplorer object. If such...
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    Windows 7 adds support for TLSv1.1 and TLSv1.2

    • 3 Comments
    Windows 7's updated crypto stack (schannel.dll, etc) offers support for TLSv1.1 and TLSv1.2. While disabled by default in IE8 (for compatibility reasons; some legacy sites will fail to connect when the updated TLS version is offered) the new protocol...
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    IE8 Problem Reports: ASP.NET Menus show blank/white

    • 0 Comments
    Q: My ASP.NET site's menus show as blank/white when my page is rendered in IE8 standards mode. The menus only work if I turn on compatibility view. What's up with that? A: This is actually a standards-compliance bug in the ASP.NET framework. A fix...
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    Enhanced Security with SEHOP

    • 2 Comments
    Windows Vista SP1 introduced an interesting new memory protection known as SEHOP, which works with other memory protection techniques (like DEP/NX , ASLR, etc) to help prevent exploitation of a specific type of memory-related vulnerability known as SEH...
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    Good news: Security innovation spreading...

    • 0 Comments
    Version 4 of the Safari web browser now supports the HTTPOnly directive for cookies introduced by IE6 SP1. Now, all major browsers support the directive, which can help mitigate the impact of XSS exploits. Safari 4 also now supports the X-FRAME-OPTIONS...
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    Vary with Care

    • 14 Comments
    About the Vary Response Header As described in the HTTP/1.1 specification ( RFC2616 ), the Vary response header allows a cache to determine if a cached (still fresh) response may be returned for a subsequent request, based on whether or not the new...
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    HTTP/HTTPS Port-Blocking in WinINET

    • 0 Comments
    Internet Explorer (actually, WinINET, the network stack beneath IE) prohibits use of certain ports for HTTP(S) connections. The intent of this blocking is to prevent Cross Service/Protocol Request Forgery attacks. For instance, an attacker could use a...
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    CSS History Probing, or: "I know where you went last week"

    • 5 Comments
    Background One of the interesting attacks which makes the rounds every few years concerns the ability of web pages to use CSS to detect whether or not certain URLs have been visited. Given a sufficiently large set of URLs to probe, a website may be able...
  • IEInternals

    Building Safer ActiveX controls: DOM Bridging

    • 0 Comments
    Over on the BlueHat blog, security researcher Manuel Caballero wrote up an interesting post on how Silverlight avoids exposing unsecured private browser APIs to abuse from RIA content. Anyone building ActiveX controls that take untrusted input should...
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