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This page documents security issues in the "View Source" feature. In particular it covers the View Source "Linkification", a new feature in Firefox 3.1. The View Source QA TestPlan provides the most complete current documentation, including bugs.


Linkification turns URLs in HREF and SRC attributes into hyperlinks which link to the source URL. The current approach is simple to the point of being crude, but it was chosen as a way to get a lot of "bang for the buck", if you will.

When a URL is "linkified", the source URL is first converted into an absolute URL (if it's not already), using the URL to the source file being used. If the source file specifies one or more BASE elements, then the base URL specified by the last BASE element is used.

Once an absolute URL has been constructed, it is turned into a "view-source:" URL. For example the URL will be turned into view-source: So clicking a link to an HTML page in page source will bring up the source for the new page, not the rendered HTML for that page.

Note that if a URL points to a text file (as determined by MIME type), then both the source URL and the view-source URL constructed from it have the same effect. So CSS and JS files linked from page source work as expected.

Currently images linked from page source do not work correctly (see [ Bug 464339). The "mailto:" and "view-source:mailto:" schemes work the same way, although that's by accident.

We need to think about what happens with javascript: links. In general, is there anyway javascript can be injected into the view-source window and run surreptitiously? What capability might this JavaScript have?

Describe the goals and objectives of the feature here.

Background links

  • Bugs related directly to the security review
    • Bug 467852 - View Source Linkification should only linkify "safe" URLs.
  • feature-tracking bug links -- these bugs document how view source is supposed to work in general.
    • Bug 15364: Add line numbers to View Source
    • Bug 17612: view-source link-browsing
    • Bug 22022: no wrapping in view source
    • Bug 39389: No context menus in "view source" window
    • Bug 49721: [RFE] View Partial Source capability
    • Bug 50877: Menu items don't work in View Source window
    • Bug 55583: view-source should show original page source (use cached source)
    • Bug 59489: Cannot print page source
    • Bug 63026: Give me the menu in View Source back
    • Bug 63137: [FIX]View Source converts tags to lower case
    • Bug 71173: find only works once in view page source window
    • Bug 77337: [FIX]view-source: does not allow viewing of many text files
    • Bug 80598: View source window does not focus the content area when it's brought up
    • Bug 85752: move viewsource search menuitems to edit and kill the search menu
    • Bug 85908: Add reload to View Page Source Window
    • Bug 99676: ctrl-e in viewsource causes composer to load highlighted source

Security and Privacy

  • What security issues do you address in your project?


  • Is system or subsystem security compromised in any way if your project's configuration files / prefs are corrupt or missing?

No. (Are there any prefs that affect View Source?)

  • Include a thorough description of the security assumptions, capabilities and any potential risks (possible attack points) being introduced by your project.


  • How are transitions in/out of Private Browsing mode handled?

Not relevant

Exported APIs

  • Please provide a table of exported interfaces (APIs, ABIs, protocols, UI, etc.)


  • Does it interoperate with a web service? How will it do so?


  • Explain the significant file formats, names, syntax, and semantics.


  • Are the externally visible interfaces documented clearly enough for a non-Mozilla developer to use them successfully?


  • Does it change any existing interfaces?


Module interactions

  • What other modules are used (REQUIRES in the makefile, interfaces)

No changes


  • What data is read or parsed by this feature
    • Document Base URLs
    • URLs in SRC and HREF attributes
  • What is the output of this feature

Same View Source as always, but now with hyperlinks

  • What storage formats are used

No storage formats


  • What failure modes or decision points are presented to the user?

Click a link or don't click a link

  • Can its files be corrupted by failures? Does it clean up any locks/files after crashes?

Files may be read from disk, but no files are written. Note that View Source in general is designed to pull files from cache if at all possible, but I'm not sure if there are any security issues to this.


  • Can the end user configure settings, via a UI or about:config? Hidden prefs? Environment variables?

Linkification isn't affected by prefs; I'm not sure about view source in general.

  • Are there build options for developers? [#ifdefs, ac_add_options, etc.]


  • What ranges for the tunable are appropriate? How are they determined?


  • What are its on-going maintenance requirements (e.g. Web links, perishable data files)?


Relationships to other projects

Are there related projects in the community?


  • If so, what is the proposal's relationship to their work? Do you depend on others' work, or vice-versa?


  • Are you updating, copying or changing functional areas maintained by other groups? How are you coordinating and communicating with them? Do they "approve" of what you propose?


Review comments

  • need to whitelist scheme? either a short static list, or at least checkLoadURI?
    • Bug 467852 - View Source Linkification should only linkify "safe" URLs.
  • javascript: in particular would be bad (but seems to be blocked?)
  • what's the principal used for data: urls?
  • what referrer gets sent?
  • Jesse thinks DNS prefetching needs to be disabled for privacy since we might linkify things that weren't actual links in the page. (<foo href=""> will get linkified).
  • make sure URI's added can't be used for script injection, extra quotes don't mess it up, etc.