MediaWiki 1.16.3 security release

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There is a new MediaWiki release available which addresses three security vulnerabilities:

  • A cross-site scripting (XSS) issue involving media uploads affecting Internet Explorer version 6 and earlier.   Note: fully addressing this issue requires web server configuration changes.  See bug 28235 and full announcement below for details (discovered by Masato Kinugawa).
  • A CSS validation problem in the wikitext parser.  This is a cross-site scripting (XSS) issue for all Internet Explorer clients, and a privacy loss issue for other clients. See bug 28450 and full announcement below for details (discovered by user Suffusion)
  • A transwiki import problem with  access control checks on form submission, which only affects wikis where this feature is enabled. For more details, see bug 28449 and full announcement below for details (discovered by MediaWiki developer Happy-Melon)

Full announcement from Tim Starling after the jump…

I would like to announce the release of MediaWiki 1.16.3, which is a security release. Three security issues were discovered.
Masato Kinugawa discovered a cross-site scripting (XSS) issue, which affects Internet Explorer clients only, and only version 6 and
earlier. Web server configuration changes are required to fix this issue. Upgrading MediaWiki will only be sufficient for people who use
Apache with AllowOverride enabled.
Due to the diversity of uploaded files that we allow, MediaWiki does not guarantee that uploaded files will be safe if they are interpreted
by the client as some arbitrary file type, such as HTML. We rely on the web server to send the correct Content-Type header, and we rely on
the web browser to respect it. This XSS issue arises due to IE 6 looking for a file extension in the query string of the URL (i.e. after the “?”), if no extension is found in path part of the URL. Masato Kinugawa discovered that the file extension in the path part can be hidden from IE 6 by substituting the “.” with “%2E”.
To fix this issue, configure your web server to deny requests with URLs that have a path part ending in a dot followed by a dangerous file extension. For example, in Apache with mod_rewrite:

RewriteEngine On
RewriteCond %{QUERY_STRING} .[a-z]{1,4}$ [nocase]
RewriteRule . - [forbidden]

Upgrading MediaWiki is necessary to fix this issue in dynamically-generated content. This issue is easier to exploit using dynamically generated content, since it requires no special privileges. Accounts on both public and private wikis can be compromised by clicking a malicious link in an email or website. For more details, see bug 28235.
Wikipedia user Suffusion of Yellow discovered a CSS validation error in the wikitext parser. This is an XSS issue for Internet Explorer clients, and a privacy loss issue for other clients since it allows the embedding of arbitrary remote images. For more details, see bug 28450.
MediaWiki developer Happy-Melon discovered that the transwiki import feature neglected to perform access control checks on form submission. The transwiki import feature is disabled by default. If it is enabled, it allows wiki pages to be copied from a remote wiki listed in $wgImportSources. The issue means that any user can trigger such an import to occur. For more details, see bug 28449.
The localisations were updated using content from
Rob Lanphier, Director of Platform Engineering
Patch to previous version (1.16.2), without interface text:
Interface text changes:
GPG signatures:
Public keys:

Archive notice: This is an archived post from, which operated under different editorial and content guidelines than Diff.

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