web commit by JamesWestby

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

diff --git a/doc/security.mdwn b/doc/security.mdwn
index 0f8861d0dbb6f99f5857828f5bd71f7453048d66..fea0eb727d655fe2c7452174b08e3d718e7aae40 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


@@ -6,33 +6,52 @@ 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
 
 # Probable holes
 

-## html attacks
+_(The list of things to fix.)_
+
+## commit spoofing

 
 

-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)).
+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 certian user.

 
 

-## image files etc attacks
+## other stuff to look at
+
+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.
+
+----
+
+# Potential gotchas
+
+_(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).
+Users 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.
 


@@ -42,34 +61,34 @@ 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
-
-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.
-

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

-A [[lock]]ed page can only be edited on the web by an admin, but
+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.
 
 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.
 

+## 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.
+

 ----
 
 # 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
 
 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.
 
 
 ## 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.
 

+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 +112,8 @@ 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
 


@@ -116,11 +136,32 @@ file not be world readable.
 
 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.
 
 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.
+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.
+
+## 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.
+
+## 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.)
+
+----

 
 # Fixed holes
 
 
 # Fixed holes
 

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

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


@@ -157,11 +198,18 @@ their own can race it.
 
 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
 
 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.
+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 by making ikiwiki refuse to read or write to files that are
-symlinks, combined with the above locking.
+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.
+
+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
 


@@ -170,17 +218,50 @@ 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.
-
-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.
+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 refuse to add any files from the
+underlaydir if a file also exists in the srcdir with the same name.
+
+## 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.
+
+## 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.