3 files changed, 68 insertions, 1 deletions
diff --git a/debian/NEWS b/debian/NEWS
index b2753c638..66b2b4299 100644
--- a/debian/NEWS
+++ b/debian/NEWS
@@ -1,3 +1,27 @@
+ikiwiki (3.20160506) UNRELEASED; urgency=medium
+
+  To mitigate CVE-2016-3714 and similar ImageMagick security vulnerabilities,
+  the [[!img]] directive is now restricted to these common web formats by
+  default:
+
+  * JPEG (.jpg, .jpeg)
+  * PNG (.png)
+  * GIF (.gif)
+  * SVG (.svg)
+
+  (In particular, by default resizing PDF files is no longer allowed.)
+
+  Additionally, resized SVG files are displayed in the browser as SVG
+  instead of being converted to PNG.
+
+  If all users who can attach images are fully trusted, this restriction
+  can be removed with the new img_allowed_formats setup option.
+  See <https://ikiwiki.info/ikiwiki/directive/img/>
+  or <file:///usr/share/doc/ikiwiki/html/ikiwiki/directive/img.html> for
+  more details.
+
+ -- Simon McVittie <smcv@debian.org>  Fri, 06 May 2016 07:07:29 +0100
+
 ikiwiki (3.20150610) unstable; urgency=low
 
   The new "emailauth" plugin allows users to authenticate using an email
diff --git a/doc/ikiwiki/directive/img.mdwn b/doc/ikiwiki/directive/img.mdwn
index fa3b40f50..a940a44b6 100644
--- a/doc/ikiwiki/directive/img.mdwn
+++ b/doc/ikiwiki/directive/img.mdwn
@@ -41,4 +41,27 @@ the page, unless overridden. Useful when including many images on a page.
 	\[[!img photo2.jpg]]
 	\[[!img photo3.jpg size=200x600]]
 
+## format support
+
+By default, the `img` directive only supports a few common web formats:
+
+* PNG (`.png`)
+* JPEG (`.jpg` or `.jpeg`)
+* GIF (`.gif`)
+* SVG (`.svg`)
+
+These additional formats can be enabled with the `img_allowed_formats`
+[[!iki setup]] option, but are disabled by default for better
+[[!iki security]]:
+
+* PDF (`.pdf`)
+* `everything` (accepts any file supported by ImageMagick: make sure
+  that only completely trusted users can
+  [[upload attachments|ikiwiki/pagespec/attachment]])
+
+For example, a wiki where only `admin()` users can upload attachments might
+use:
+
+    img_allowed_formats: [png, jpeg, gif, svg, pdf]
+
 [[!meta robots="noindex, follow"]]
diff --git a/doc/security.mdwn b/doc/security.mdwn
index d5a0266cd..6d4841fe6 100644
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -178,7 +178,8 @@ the same standards as the rest of ikiwiki, but with that said, here are
 some security notes for them.
 
 * The [[plugins/img]] plugin assumes that imagemagick/perlmagick are secure
-  from malformed image attacks. Imagemagick has had security holes in the
+  from malformed image attacks for at least the formats listed in
+  `img_allowed_formats`. Imagemagick has had security holes in the
   past. To be able to exploit such a hole, a user would need to be able to
   upload images to the wiki.
 
@@ -506,3 +507,22 @@ The hole was reported on March 24th, a fix was developed on March 27th,
 and the fixed version 3.20150329 was released on the 29th. A fix was backported
 to Debian jessie as version 3.20141016.2 and to Debian wheezy as version
 3.20120629.2. An upgrade is recommended for sites using CGI and openid.
+
+## XSS via error messages
+
+CGI error messages did not escape HTML meta-characters, potentially
+allowing an attacker to carry out cross-site scripting by directing a
+user to a URL that would result in a crafted ikiwiki error message. This
+was discovered on 4 May by the ikiwiki developers, and the fixed version
+3.20160506 was released on 6 May. An upgrade is recommended for sites using
+the CGI.
+
+## ImageMagick CVE-2016–3714 ("ImageTragick")
+
+ikiwiki 3.20160506 attempts to mitigate [[!cve CVE-2016-3714]] and any
+future ImageMagick vulnerabilities that resemble it, by restricting the
+image formats that the [[ikiwiki/directive/img]] directive is willing to
+resize. An upgrade is recommended for sites where an untrusted user is
+able to attach images. Upgrading ImageMagick to a version where
+CVE-2016-3714 has been fixed is also recommended, but at the time of
+writing no such version is available.