web commit by JeroenSchot

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

diff --git a/doc/security.mdwn b/doc/security.mdwn
index c2ddc2424105d8e84e04d38ee06629411bc3eab3..3743adea1e61b5225520d4f889b80d0208ad0ca3 100644 (file)
--- a/doc/security.mdwn
+++ b/doc/security.mdwn
@@ -44,12 +44,21 @@ this wiki, BTW.
 
 ## svn commit logs
 
 
 ## svn commit logs
 

-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.
+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..
+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 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
 ----
 
 # Hopefully non-holes


@@ -84,20 +93,7 @@ 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 it runs with taint checks on of course..
-
-## 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.
+wiki admin and untainted filenames. And it runs with taint checks on of course..

 
 ## cgi data security
 
 
 ## cgi data security
 


@@ -109,18 +105,35 @@ 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/". 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.
 
 ## 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.
 

-## CGI::Session security
+# Fixed holes

 
 

-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.
+_(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
 


@@ -130,6 +143,45 @@ 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.
-
-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
+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.