fixes

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

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 7b056fd6c1fecbb4101cb8f9c5ba9dbf3efb867e..c7a6fcd69dd0d91df051d793ce2d1a0bd2299a52 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -6,10 +6,12 @@ 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.
 

+# Probable holes
+

 ## html attacks
 
 ikiwiki does not attempt to do any santization of the html on the wiki.
 ## html attacks
 
 ikiwiki does not attempt to do any santization of the html on the wiki.

-MarkDown allows embedding of arbitrary html into a markdown document. If
+[[MarkDown]] allows embedding of arbitrary html into a markdown document. If

 you let anyone else edit files on the wiki, then anyone can have fun exploiting
 the web browser bug of the day. This type of attack is typically referred
 to as an XSS attack ([google](http://www.google.com/search?q=xss+attack)).
 you let anyone else edit files on the wiki, then anyone can have fun exploiting
 the web browser bug of the day. This type of attack is typically referred
 to as an XSS attack ([google](http://www.google.com/search?q=xss+attack)).


@@ -18,22 +20,9 @@ to as an XSS attack ([google](http://www.google.com/search?q=xss+attack)).
 
 If it enounters a file type it does not understand, ikiwiki just copies it
 into place. So if you let users add any kind of file they like, they can
 
 If it enounters a file type it does not understand, ikiwiki just copies it
 into place. So if you let users add any kind of file they like, they can

-upload images, movies, windows executables, etc. If these files exploit
-security holes in the browser of someone who's viewing the wiki, that can
-be a security problem.
-
-## exploting ikiwiki with bad content
+upload images, movies, windows executables, css files, etc. If these files exploit security holes in the browser of someone who's viewing the wiki, that can be a security problem.

 
 

-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;
-the only data that is not subject to full taint checking is the names of
-files, and filenames are sanitised.
-
-## cgi scripts
-
-ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
-rather, the script is published, but it's not marked executable, so
-hopefully your web server will not run it.
+Of course nobody else seems to worry about this in other wikis, so should we?

 
 ## web server attacks
 
 
 ## web server attacks
 


@@ -41,16 +30,108 @@ If your web server does any parsing of special sorts of files (for example,
 server parsed html files), then if you let anyone else add files to the wiki,
 they can try to use this to exploit your web server.
 
 server parsed html files), then if you let anyone else add files to the wiki,
 they can try to use this to exploit your web server.
 

-## --gen-wrapper might generate insecure wrappers
+## 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.
+
+So it's best if only one person can ever write to those directories.
+
+## 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.
+
+## svn commit logs
+
+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.
+
+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 somewhat by revision number scanning, since the forged revisions would duplicate the numbers of unforged ones. Or subversion could fix svn log to indent commit messages, which would make such forgery impossible..
+
+ikiwiki escapes any html in svn commit logs to prevent other mischief.
+
+## page locking can be bypassed via direct svn commits
+
+A [[lock]]ed 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.
+
+----
+
+# Hopefully non-holes
+
+(AKA, the assumptions that will be the root of most security holes...)
+
+## exploting 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.
+
+## publishing cgi scripts
+
+ikiwiki does not allow cgi scripts to be published as part of the wiki. Or
+rather, the script is published, but it's not marked executable (except in
+the case of "destination directory file replacement" below), so hopefully
+your web server will not run it.
+
+## suid wrappers

 
 

-ikiwiki --gen-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.
 
 If the wrapper script is made suid, then any bugs in this wrapper would be
 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.
 
 If the wrapper script is made suid, then any bugs in this wrapper would be

-security holes. The wrapper is written as securely as I know how and
-there's been no problem yet.
+security holes. The wrapper is written as securely as I know how, is based
+on code that has a history of security use long before ikiwiki, and there's
+been no problem yet.
+
+## 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..
+
+## cgi data security
+
+When ikiwiki runs as a cgi to edit a page, it is passed the name of the
+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 "/"
+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.
+
+## CGI::Session security
+
+I've audited this module and it is massively insecure by default. ikiwiki
+uses it in one of the few secure ways; by forcing it to write to a
+directory it controls (and not /tmp) and by setting a umask that makes the
+file not be world readable.
+
+## 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.
+
+# Fixed holes
+
+_(Unless otherwise noted, these were discovered and immediatey fixed by the ikiwiki developers.)_
+
+## destination directory file replacement
+
+Any file in the destination directory that is a valid page filename can be
+replaced, even if it was not originally rendered from a page. For example,
+ikiwiki.cgi could be edited in the wiki, and it would write out a
+replacement. File permission is preseved. Yipes!
+
+This was fixed by making ikiwiki check if the file it's writing to exists;
+if it does then it has to be a file that it's aware of creating before, or
+it will refuse to create it.
+
+Still, this sort of attack is something to keep in mind.

 
 ## symlink attacks
 
 
 ## symlink attacks
 


@@ -58,28 +139,24 @@ Could a committer trick ikiwiki into following a symlink and operating on
 some other tree that it shouldn't? svn supports symlinks, so one can get
 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
 tell it to follow symlinks, but it might be possible to race replacing a
 some other tree that it shouldn't? svn supports symlinks, so one can get
 into the repo. ikiwiki uses File::Find to traverse the repo, and does not
 tell it to follow symlinks, but it might be possible to race replacing a

-directory with a symlink and trick it into following.
+directory with a symlink and trick it into following the link.

 
 

-It would certianly be possible to start out with a directory, let ikiwiki
-run and find a file in there, then replace it with a symlink, and ikiwiki
-would then go ahead and follow the symlink when it went to open that file
-to read it. If it was some private file and was running suid, that could be
-bad.
+Also, if someone checks in a symlink to /etc/passwd, ikiwiki would read and
+publish that, which could be used to expose files a committer otherwise
+wouldn't see.

 
 

-TODO: seems that locking to prevent more than one ikiwiki run at a time
-would both fix this and is a good idea in general. With locking, an
-attacker couldn't get ikiwiki to svn up while another instance was running.
+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.

 
 

-Even with locking, if an attacker has local write access to the checkout,
-they could still fool ikiwiki using similar races. So it's best if only one
-person can ever write to the checkout that ikiwiki compiles the moo from.
+## symlink + cgi attacks

 
 

-## cgi security
+Similarly, a svn 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
+page from the web, which follows the symlink when reading the page, and
+again when saving the changed page.

 
 

-When ikiwiki runs as a cgi to edit a page, it is passed the name of the
-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 "/"
-or contain ".." or "/.svn/". Annoyingly ad-hoc, this kind of code is where
-security holes breed.
+This was fixed by making ikiwiki refuse to read or write to files that are
+symlinks, combined with the above locking.