web commit by joey

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

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 72568a34801ce5da723625f026e8187e71a561b0..766b8bee4bd6a61ecb711fa579a011e692cf2b55 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -6,33 +6,51 @@ 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
 
 # Probable holes
 

-## html attacks
+_(The list of things to fix.)_
+
+## 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 by using svn log --xml.
+
+ikiwiki escapes any html in svn commit logs to prevent other mischief.
+
+----

 
 

-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
-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)).
+# Potential gotchas

 
 

-## image files etc attacks
+_(Things not to do.)_
+
+## image file etc attacks

 
 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, 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.
+upload images, movies, windows executables, css files, etc (though not html
+files). If these files exploit security holes in the browser of someone
+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?
 

-## web server attacks
-
-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.
+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.

 
 ## 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 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 write to those directories.
 


@@ -42,19 +60,24 @@ 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.
 
 Just don't do it. [[ikiwiki.setup]] is *not* used as the setup file for
 this wiki, BTW.
 

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

 
 

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

 
 

-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..
+## web server attacks

 
 

-ikiwiki escapes any html in svn commit logs to prevent other mischief.
+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.

 
 ----
 
 # Hopefully non-holes
 
 
 ----
 
 # Hopefully non-holes
 

-(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
 
 
 ## exploting ikiwiki with bad content
 


@@ -84,7 +107,8 @@ been no problem yet.
 
 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
 
 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..
+wiki admin and untainted filenames. And it runs with taint checks on of
+course..

 
 ## cgi data security
 
 
 ## cgi data security
 


@@ -109,7 +133,21 @@ 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.
 
 Cracking the password only allows editing the wiki as that user though.
 If you care, you can use https, I suppose.
 

-# Fixed holes.
+## XSS holes in CGI output
+
+ikiwiki has not yet 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.
+
+----
+
+# Fixed holes
+
+_(Unless otherwise noted, these were discovered and immediatey fixed by the
+ikiwiki developers.)_

 
 ## destination directory file replacement
 
 
 ## destination directory file replacement
 


@@ -132,6 +170,49 @@ 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 the link.
 
 tell it to follow symlinks, but it might be possible to race replacing a
 directory with a symlink and trick it into following the link.
 

-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.
+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.
+
+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.
+
+## symlink + cgi attacks
+
+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.
+
+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.
+
+## underlaydir override attacks
+
+ikiwiki also scans an underlaydir for pages, this is used to provide stock
+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
+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.
+
+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`).
+
+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.
+
+## XSS attacks in page content

 
 

-To avoid this, ikiwiki will avoid reading files that are symlinks, 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.
\ No newline at end of file
+ikiwiki supports [[HtmlSanitization]], though it can be turned off.