Merge branch 'master' of ssh://git.ikiwiki.info/srv/git/ikiwiki.info

[git.ikiwiki.info.git] / doc / security.mdwn

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 73d98a3ae5fcf88c1dbcbe4b0ba983f853ad54e8..3924186c2120c9371b1f55b648c4a760a0a5d6d3 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -1,4 +1,4 @@
-Let's do an ikiwiki security analysis..
+Let's do an ikiwiki security analysis.

 
 If you are using ikiwiki to render pages that only you can edit, do not
 generate any wrappers, and do not use the cgi, then there are no more
 
 If you are using ikiwiki to render pages that only you can edit, do not
 generate any wrappers, and do not use the cgi, then there are no more


@@ -6,23 +6,24 @@ security issues with this program than with cat(1). If, however, you let
 others edit pages in your wiki, then some possible security issues do need
 to be kept in mind.
 
 others edit pages in your wiki, then some possible security issues do need
 to be kept in mind.
 

+[[!toc levels=2]]
+

 ----
 
 # Probable holes
 
 _(The list of things to fix.)_
 
 ----
 
 # Probable holes
 
 _(The list of things to fix.)_
 

-## svn commit logs
+## commit spoofing

 
 

-Anyone with svn commit access can forge "web commit from foo" and make it
-appear on [[RecentChanges]] like foo committed. One way to avoid this would
-be to limit web commits to those done by a certian user.
+Anyone with direct commit access can forge "web commit from foo" and
+make it appear on [[RecentChanges]] like foo committed. One way to avoid
+this would be to limit web commits to those done by a certain user.

 
 

-It's actually possible to force a whole series of svn commits to appear to
-have come just before yours, by forging svn log output. This could be
-guarded against by using svn log --xml.
+## other stuff to look at

 
 

-ikiwiki escapes any html in svn commit logs to prevent other mischief.
+I need to audit the git backend a bit, and have been meaning to
+see if any CRLF injection type things can be done in the CGI code.

 
 ----
 
 
 ----
 


@@ -40,32 +41,39 @@ who's viewing the wiki, that can be a security problem.
 
 Of course nobody else seems to worry about this in other wikis, so should we?
 
 
 Of course nobody else seems to worry about this in other wikis, so should we?
 

-Currently only people with direct svn commit access can upload such files
-(and if you wanted to you could block that with a svn pre-commit hook).
-Wsers with only web commit access are limited to editing pages as ikiwiki
-doesn't support file uploads from browsers (yet), so they can't exploit
-this.
+People with direct commit access can upload such files
+(and if you wanted to you could block that with a pre-commit hook).
+
+The attachments plugin is not enabled by default. If you choose to
+enable it, you should make use of its powerful abilities to filter allowed
+types of attachments, and only let trusted users upload.
+
+It is possible to embed an image in a page edited over the web, by using
+`img src="data:image/png;"`. Ikiwiki's htmlscrubber only allows `data:`
+urls to be used for `image/*` mime types. It's possible that some broken
+browser might ignore the mime type and if the data provided is not an
+image, instead run it as javascript, or something evil like that. Hopefully
+not many browsers are that broken.

 
 ## multiple accessors of wiki directory
 
 
 ## multiple accessors of wiki directory
 

-If multiple people can write to the source directory ikiwiki is using, or
-to the destination directory it writes files to, then one can cause trouble
-for the other when they run ikiwiki through symlink attacks.
+If multiple people can directly write to the source directory ikiwiki is
+using, or to the destination directory it writes files to, then one can
+cause trouble for the other when they run ikiwiki through symlink attacks.

 
 

-So it's best if only one person can ever write to those directories.
+So it's best if only one person can ever directly write to those directories.

 
 ## setup files
 
 
 ## setup files
 

-Setup files are not safe to keep in subversion with the rest of the wiki.
-Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
-this wiki, BTW.
+Setup files are not safe to keep in the same revision control repository
+with the rest of the wiki. Just don't do it.

 
 

-## page locking can be bypassed via direct svn commits
+## page locking can be bypassed via direct commits

 
 

-A locked page can only be edited on the web by an admin, but
-anyone who is allowed to commit direct to svn can bypass this. This is by
-design, although a subversion pre-commit hook could be used to prevent
-editing of locked pages when using subversion, if you really need to.
+A locked page can only be edited on the web by an admin, but anyone who is
+allowed to commit directly to the repository can bypass this. This is by
+design, although a pre-commit hook could be used to prevent editing of
+locked pages, if you really need to.

 
 ## web server attacks
 
 
 ## web server attacks
 


@@ -79,11 +87,15 @@ they can try to use this to exploit your web server.
 
 _(AKA, the assumptions that will be the root of most security holes...)_
 
 
 _(AKA, the assumptions that will be the root of most security holes...)_
 

-## exploting ikiwiki with bad content
+## exploiting ikiwiki with bad content

 
 Someone could add bad content to the wiki and hope to exploit ikiwiki.
 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
 
 
 Someone could add bad content to the wiki and hope to exploit ikiwiki.
 Note that ikiwiki runs with perl taint checks on, so this is unlikely.
 

+One fun thing in ikiwiki is its handling of a PageSpec, which involves
+translating it into perl and running the perl. Of course, this is done
+*very* carefully to guard against injecting arbitrary perl code.
+

 ## publishing cgi scripts
 
 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
 ## publishing cgi scripts
 
 ikiwiki does not allow cgi scripts to be published as part of the wiki. Or


@@ -93,7 +105,7 @@ your web server will not run it.
 
 ## suid wrappers
 
 
 ## suid wrappers
 

-ikiwiki --wrapper is intended to generate a wrapper program that
+`ikiwiki --wrapper` is intended to generate a wrapper program that

 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
 for example to be used in a [[post-commit]] hook by people who cannot write
 to the html pages, etc.
 runs ikiwiki to update a given wiki. The wrapper can in turn be made suid,
 for example to be used in a [[post-commit]] hook by people who cannot write
 to the html pages, etc.


@@ -106,9 +118,13 @@ been no problem yet.
 ## shell exploits
 
 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use
 ## shell exploits
 
 ikiwiki does not expose untrusted data to the shell. In fact it doesn't use

-system() at all, and the only use of backticks is on data supplied by the
-wiki admin and untainted filenames. And it runs with taint checks on of
-course..
+`system(3)` at all, and the only use of backticks is on data supplied by the
+wiki admin and untainted filenames. 
+
+Ikiwiki was developed and used for a long time with perl's taint checking
+turned on as a second layer of defense against shell and other exploits. Due
+to a strange [bug](http://bugs.debian.org/411786) in perl, taint checking
+is currently disabled for production builds of ikiwiki.

 
 ## cgi data security
 
 
 ## cgi data security
 


@@ -117,8 +133,8 @@ page to edit. It has to make sure to sanitise this page, to prevent eg,
 editing of ../../../foo, or editing of files that are not part of the wiki,
 such as subversion dotfiles. This is done by sanitising the filename
 removing unallowed characters, then making sure it doesn't start with "/"
 editing of ../../../foo, or editing of files that are not part of the wiki,
 such as subversion dotfiles. This is done by sanitising the filename
 removing unallowed characters, then making sure it doesn't start with "/"

-or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
-security holes breed. It needs a test suite at the very least.
+or contain ".." or "/.svn/", etc. Annoyingly ad-hoc, this kind of code is
+where security holes breed. It needs a test suite at the very least.

 
 ## CGI::Session security
 
 
 ## CGI::Session security
 


@@ -129,24 +145,47 @@ file not be world readable.
 
 ## cgi password security
 
 
 ## cgi password security
 

-Login to the wiki involves sending a password in cleartext over the net.
-Cracking the password only allows editing the wiki as that user though.
-If you care, you can use https, I suppose.
+Login to the wiki using [[plugins/passwordauth]] involves sending a password
+in cleartext over the net. Cracking the password only allows editing the wiki
+as that user though. If you care, you can use https, I suppose. If you do use
+https either for all of the wiki, or just the cgi access, then consider using
+the sslcookie option. Using [[plugins/openid]] is a potentially better option.

 
 ## XSS holes in CGI output
 
 
 ## XSS holes in CGI output
 

-ikiwiki has not yet been audited to ensure that all cgi script input/output
+ikiwiki has been audited to ensure that all cgi script input/output

 is sanitised to prevent XSS attacks. For example, a user can't register
 with a username containing html code (anymore).
 
 It's difficult to know for sure if all such avenues have really been
 closed though.
 
 is sanitised to prevent XSS attacks. For example, a user can't register
 with a username containing html code (anymore).
 
 It's difficult to know for sure if all such avenues have really been
 closed though.
 

+## HTML::Template security
+
+If the [[plugins/template]] plugin is enabled, users can modify templates
+like any other part of the wiki. This assumes that HTML::Template is secure
+when used with untrusted/malicious templates. (Note that includes are not
+allowed, so that's not a problem.)
+
+----
+
+# Plugins
+
+The security of [[plugins]] depends on how well they're written and what
+external tools they use. The plugins included in ikiwiki are all held to
+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
+  past. To be able to exploit such a hole, a user would need to be able to
+  upload images to the wiki.
+

 ----
 
 # Fixed holes
 
 ----
 
 # Fixed holes
 

-_(Unless otherwise noted, these were discovered and immediatey fixed by the
+_(Unless otherwise noted, these were discovered and immediately fixed by the

 ikiwiki developers.)_
 
 ## destination directory file replacement
 ikiwiki developers.)_
 
 ## destination directory file replacement


@@ -176,20 +215,26 @@ wouldn't see.
 
 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
 uses locking to prevent more than one instance running at a time. The lock
 
 To avoid this, ikiwiki will skip over symlinks when scanning for pages, and
 uses locking to prevent more than one instance running at a time. The lock

-prevents one ikiwiki from running a svn up at the wrong time to race
-another ikiwiki. So only attackers who can write to the working copy on
-their own can race it.
+prevents one ikiwiki from running a svn up/git pull/etc at the wrong time
+to race another ikiwiki. So only attackers who can write to the working
+copy on their own can race it.

 
 ## symlink + cgi attacks
 
 
 ## symlink + cgi attacks
 

-Similarly, a svn commit of a symlink could be made, ikiwiki ignores it
+Similarly, a commit of a symlink could be made, ikiwiki ignores it

 because of the above, but the symlink is still there, and then you edit the
 because of the above, but the symlink is still there, and then you edit the

-page from the web, which follows the symlink when reading the page, and
-again when saving the changed page.
+page from the web, which follows the symlink when reading the page
+(exposing the content), and again when saving the changed page (changing
+the content).
+
+This was fixed for page saving by making ikiwiki refuse to write to files
+that are symlinks, or that are in subdirectories that are symlinks,
+combined with the above locking.

 
 

-This was fixed by making ikiwiki refuse to read or write to files that are
-symlinks, or that are in subdirectories that are symlinks, combined with
-the above locking.
+For page editing, it's fixed by ikiwiki checking to make sure that it
+already has found a page by scanning the tree, before loading it for
+editing, which as described above, also is done in a way that avoids
+symlink attacks.

 
 ## underlaydir override attacks
 
 
 ## underlaydir override attacks
 


@@ -198,22 +243,187 @@ pages to all wikis w/o needing to copy them into the wiki. Since ikiwiki
 internally stores only the base filename from the underlaydir or srcdir,
 and searches for a file in either directory when reading a page source,
 there is the potential for ikiwiki's scanner to reject a file from the
 internally stores only the base filename from the underlaydir or srcdir,
 and searches for a file in either directory when reading a page source,
 there is the potential for ikiwiki's scanner to reject a file from the

-srcdir for some reason (such as it being a symlink), find a valid copy of
-the file in the underlaydir, and then when loading the file, mistekenly
-load the bad file from the srcdir.
+srcdir for some reason (such as it being contained in a directory that is
+symlinked in), find a valid copy of the file in the underlaydir, and then
+when loading the file, mistakenly load the bad file from the srcdir.

 
 

-This attack is avoided by making ikiwiki scan the srcdir first, and refuse
-to add any files from the underlaydir if a file also exists in the srcdir
-with the same name. **But**, note that this assumes that any given page can
-be produced from a file with only one name (`page.mdwn` => `page.html`).
+This attack is avoided by making ikiwiki refuse to add any files from the
+underlaydir if a file also exists in the srcdir with the same name.

 
 

-If it's possible for files with different names to produce a given page, it
-would still be possible to use this attack to confuse ikiwiki into
-rendering the wrong thing. This is not currently possible, but must be kept
-in mind in the future when for example adding support for generating html
-pages from source with some other extension.
+## multiple page source issues
+
+Note that I previously worried that underlay override attacks could also be
+accomplished if ikiwiki were extended to support other page markup
+languages besides markdown. However, a closer look indicates that this is
+not a problem: ikiwiki does preserve the file extension when storing the
+source filename of a page, so a file with another extension that renders to
+the same page name can't bypass the check. Ie, ikiwiki won't skip foo.rst
+in the srcdir, find foo.mdwn in the underlay, decide to render page foo and
+then read the bad foo.mdwn. Instead it will remember the .rst extension and
+only render a file with that extension.

 
 ## XSS attacks in page content
 
 ikiwiki supports protecting users from their own broken browsers via the
 [[plugins/htmlscrubber]] plugin, which is enabled by default.
 
 ## XSS attacks in page content
 
 ikiwiki supports protecting users from their own broken browsers via the
 [[plugins/htmlscrubber]] plugin, which is enabled by default.

+
+## svn commit logs
+
+It's was possible to force a whole series of svn commits to appear to
+have come just before yours, by forging svn log output. This was
+guarded against by using svn log --xml.
+
+ikiwiki escapes any html in svn commit logs to prevent other mischief.
+
+## XML::Parser
+
+XML::Parser is used by the aggregation plugin, and has some security holes. 
+Bug #[378411](http://bugs.debian.org/378411) does not
+seem to affect our use, since the data is not encoded as utf-8 at that
+point. #[378412](http://bugs.debian.org/378412) could affect us, although it
+doesn't seem very exploitable. It has a simple fix, and has been fixed in
+Debian unstable.
+
+## include loops
+
+Various directives that cause one page to be included into another could
+be exploited to DOS the wiki, by causing a loop. Ikiwiki has always guarded
+against this one way or another; the current solution should detect all
+types of loops involving preprocessor directives.
+
+## Online editing of existing css and images
+
+A bug in ikiwiki allowed the web-based editor to edit any file that was in
+the wiki, not just files that are page sources. So an attacker (or a
+genuinely helpful user, which is how the hole came to light) could edit
+files like style.css. It is also theoretically possible that an attacker
+could have used this hole to edit images or other files in the wiki, with
+some difficulty, since all editing would happen in a textarea.
+
+This hole was discovered on 10 Feb 2007 and fixed the same day with the
+release of ikiwiki 1.42. A fix was also backported to Debian etch, as
+version 1.33.1. I recommend upgrading to one of these versions if your wiki
+allows web editing.
+
+## html insertion via title
+
+Missing html escaping of the title contents allowed a web-based editor to
+insert arbitrary html inside the title tag of a page. Since that part of
+the page is not processed by the htmlscrubber, evil html could be injected.
+
+This hole was discovered on 21 March 2007 and fixed the same day (er, hour) 
+with the release of ikiwiki 1.46. A fix was also backported to Debian etch,
+as version 1.33.2. I recommend upgrading to one of these versions if your
+wiki allows web editing or aggregates feeds.
+
+## javascript insertion via meta tags
+
+It was possible to use the meta plugin's meta tags to insert arbitrary
+url contents, which could be used to insert stylesheet information
+containing javascript. This was fixed by sanitising meta tags.
+
+This hole was discovered on 21 March 2007 and fixed the same day
+with the release of ikiwiki 1.47. A fix was also backported to Debian etch,
+as version 1.33.3. I recommend upgrading to one of these versions if your
+wiki can be edited by third parties.
+
+## insufficient checking for symlinks in srcdir path
+
+Ikiwiki did not check if path to the srcdir to contained a symlink. If an
+attacker had commit access to the directories in the path, they could
+change it to a symlink, causing ikiwiki to read and publish files that were
+not intended to be published. (But not write to them due to other checks.)
+
+In most configurations, this is not exploitable, because the srcdir is
+checked out of revision control, but the directories leading up to it are
+not. Or, the srcdir is a single subdirectory of a project in revision
+control (ie, `ikiwiki/doc`), and if the subdirectory were a symlink,
+ikiwiki would still typically not follow it.
+
+There are at least two configurations where this is exploitable:
+
+* If the srcdir is a deeper subdirectory of a project. For example if it is
+  `project/foo/doc`, an an attacker can replace `foo` with a symlink to a
+  directory containing a `doc` directory (not a symlink), then ikiwiki
+  would follow the symlink.
+* If the path to the srcdir in ikiwiki's configuration ended in "/", 
+  and the srcdir is a single subdirectory of a project, (ie,
+  `ikiwiki/doc/`), the srcdir could be a symlink and ikiwiki would not
+  notice.
+
+This security hole was discovered on 26 November 2007 and fixed the same
+day with the release of ikiwiki 2.14. I recommend upgrading to this version
+if your wiki can be committed to by third parties. Alternatively, don't use
+a trailing slash in the srcdir, and avoid the (unusual) configurations that
+allow the security hole to be exploited.
+
+## javascript insertion via uris
+
+The htmlscrubber did not block javascript in uris. This was fixed by adding
+a whitelist of valid uri types, which does not include javascript. 
+([[!cve CVE-2008-0809]]) Some urls specifyable by the meta plugin could also
+theoretically have been used to inject javascript; this was also blocked
+([[!cve CVE-2008-0808]]).
+
+This hole was discovered on 10 February 2008 and fixed the same day
+with the release of ikiwiki 2.31.1. (And a few subsequent versions..)
+A fix was also backported to Debian etch, as version 1.33.4. I recommend
+upgrading to one of these versions if your wiki can be edited by third
+parties.
+
+## Cross Site Request Forging
+
+Cross Site Request Forging could be used to constuct a link that would
+change a logged-in user's password or other preferences if they clicked on
+the link. It could also be used to construct a link that would cause a wiki
+page to be modified by a logged-in user. ([[!cve CVE-2008-0165]])
+
+These holes were discovered on 10 April 2008 and fixed the same day with
+the release of ikiwiki 2.42. A fix was also backported to Debian etch, as
+version 1.33.5. I recommend upgrading to one of these versions.
+
+## Cleartext passwords
+
+Until version 2.48, ikiwiki stored passwords in cleartext in the `userdb`.
+That risks exposing all users' passwords if the file is somehow exposed. To
+pre-emtively guard against that, current versions of ikiwiki store password
+hashes (using Eksblowfish).
+
+If you use the [[plugins/passwordauth]] plugin, I recommend upgrading to
+ikiwiki 2.48, installing the [[!cpan Authen::Passphrase]] perl module, and running
+`ikiwiki-transition hashpassword` to replace all existing cleartext passwords
+with strong blowfish hashes. 
+
+You might also consider changing to [[plugins/openid]], which does not 
+require ikiwiki deal with passwords at all, and does not involve users sending
+passwords in cleartext over the net to log in, either.
+
+## Empty password security hole
+
+This hole allowed ikiwiki to accept logins using empty passwords, to openid
+accounts that didn't use a password. It was introduced in version 1.34, and
+fixed in version 2.48. The [bug](http://bugs.debian.org/483770) was
+discovered on 30 May 2008 and fixed the same day. ([[!cve CVE-2008-0169]])
+
+I recommend upgrading to 2.48 immediatly if your wiki allows both password
+and openid logins.
+
+## Malformed UTF-8 DOS
+
+Feeding ikiwiki page sources containing certian forms of malformed UTF-8
+can cause it to crash. This can potentially be used for a denial of service
+attack.
+
+intrigeri discovered this problem on 12 Nov 2008 and a patch put in place
+later that day, in version 2.70. The fix was backported to testing as version
+2.53.3, and to stable as version 1.33.7.
+
+## Insufficient blacklisting in teximg plugin
+
+Josh Triplett discovered on 28 Aug 2009 that the teximg plugin's
+blacklisting of insecure TeX commands was insufficient; it could be
+bypassed and used to read arbitrary files. This was fixed by
+enabling TeX configuration options that disallow unsafe TeX commands.
+The fix was released on 30 Aug 2009 in version 3.1415926, and was
+backported to stable in version 2.53.4. If you use the teximg plugin,
+I recommend upgrading. ([[!cve CVE-2009-2944]])