mod_dav_svn is vunerable to a remotely triggerable segfault DoS vulnerability
when SVNListParentPath is on.
Summary:
========
Subversion's mod_dav_svn Apache HTTPD server module will crash when it
receives an OPTIONS request against the server root and Subversion is
configured to handle the server root and SVNListParentPath is on.
This can lead to a DoS. There are no known instances of this
problem being exploited in the wild, but the details of how to exploit
it have been disclosed on the Subversion development mailing list.
Known vulnerable:
=================
Subversion HTTPD servers 1.3.0 through 1.7.14 (inclusive)
Subversion HTTPD servers 1.8.0 through 1.8.5 (inclusive)
Known fixed:
============
Subversion 1.7.15 (not publicly released)
Subversion 1.7.16
Subversion 1.8.6-1.8.7 (not publicly released)
Subversion 1.8.8
svnserve (any version) is not vulnerable
Details:
========
When Subversion is configured on the root path of the server and the
SVNListParentPath directive is set to on then the following commands
will trigger a segfault:
svn list http://svn.example.com/
svn lock http://svn.example.com/
This occurs because when mod_dav_svn attempts to calculate the parent
path of the request is ends up setting a NULL pointer (since there can be
no parent of the server root URI), which is later assumed to be valid memory.
When Subversion is configured on any Location other than "/" (e.g. "/svn")
then the problem does not occur since the parent of the path can be
calculated and stored in memory.
Severity:
=========
CVSSv2 Base Score: 4.3
CVSSv2 Base Vector: AV:N/AC:M/Au:N/C:N/I:N/A:P
We consider this to be a medium risk vulnerability. Repositories which
allow for anonymous reads will be vulnerable without authentication.
However, we believe the required configuration is relatively rare. Most
systems are not hosting Subversion on the root path of the server and
only a small number of those have the SVNListParentPath configuration on.
A remote attacker may be able to crash a Subversion server. Many Apache
servers will respawn the listener processes, but a determined attacker
will be able to crash these processes as they appear, denying service to
legitimate users. Servers using threaded MPMs will close the connection
on other clients being served by the same process that services the
OPTIONS request from the attacker. In either case there is an increased
processing impact of restarting a process and the cost of per process
caches being lost.
Recommendations:
================
We recommend all users to upgrade to Subversion 1.8.8. Users of
Subversion 1.7.x or 1.8.x who are unable to upgrade may apply the
included patch.
New Subversion packages can be found at:
http://subversion.apache.org/packages.html
Administrators that wish to protect against this without patching
immediately can apply the following configuration to their httpd.conf
file:
[[[
Order Deny,Allow
Deny from all
]]]
CAUTION: The above configuration should only be used when Subversion is
enabled on the root location in a parent path configuration. For example the
following is the minimal configuration that matches this case:
[[
DAV svn
SVNParentPath /var/svn
]]
In this case it will not block any useful requests and can be used without
concern that it will break anything. If Subversion is running on any other
path or is not being used in a parent path configuration this configuration
should not be applied as these configurations are not vulnerable and it can
break functionality of Subversion or other applications being served from the
same httpd.
References:
===========
CVE-2014-0032 (Subversion)
Report on dev mailing list: https://mail-archives.apache.org/mod_mbox/subversion-dev/201401.mbox/%3CCANvU9scLHr2yOLABW8q6_wNzhEf7pWM%3DNiavGcobqvUuyhKyAA%40mail.gmail.com%3E
Reported by:
============
Lieven Govaerts
Patches:
========
Patch against 1.7.14:
[[[
Index: subversion/mod_dav_svn/repos.c
===================================================================
--- subversion/mod_dav_svn/repos.c (revision 1558691)
+++ subversion/mod_dav_svn/repos.c (revision 1558692)
@@ -1959,6 +1959,25 @@
of private resource, iff the SVNListParentPath directive is 'on'. */
if (dav_svn__is_parentpath_list(r))
{
+ /* Only allow GET and HEAD on the parentpath resource
+ * httpd uses the same method_number for HEAD as GET */
+ if (r->method_number != M_GET)
+ {
+ int status;
+
+ /* Marshall the error back to the client by generating by
+ * way of the dav_svn__error_response_tag trick. */
+ err = dav_svn__new_error(r->pool, HTTP_METHOD_NOT_ALLOWED,
+ SVN_ERR_APMOD_MALFORMED_URI,
+ "The URI does not contain the name "
+ "of a repository.");
+ /* can't use r->allowed since the default handler isn't called */
+ apr_table_setn(r->headers_out, "Allow", "GET,HEAD");
+ status = dav_svn__error_response_tag(r, err);
+
+ return dav_push_error(r->pool, status, err->error_id, NULL, err);
+ }
+
err = get_parentpath_resource(r, resource);
if (err)
return err;
]]]
Patch against 1.8.5:
[[[
Index: subversion/mod_dav_svn/repos.c
===================================================================
--- subversion/mod_dav_svn/repos.c (revision 1558291)
+++ subversion/mod_dav_svn/repos.c (revision 1558292)
@@ -1971,6 +1971,25 @@
of private resource, iff the SVNListParentPath directive is 'on'. */
if (dav_svn__is_parentpath_list(r))
{
+ /* Only allow GET and HEAD on the parentpath resource
+ * httpd uses the same method_number for HEAD as GET */
+ if (r->method_number != M_GET)
+ {
+ int status;
+
+ /* Marshall the error back to the client by generating by
+ * way of the dav_svn__error_response_tag trick. */
+ err = dav_svn__new_error(r->pool, HTTP_METHOD_NOT_ALLOWED,
+ SVN_ERR_APMOD_MALFORMED_URI,
+ "The URI does not contain the name "
+ "of a repository.");
+ /* can't use r->allowed since the default handler isn't called */
+ apr_table_setn(r->headers_out, "Allow", "GET,HEAD");
+ status = dav_svn__error_response_tag(r, err);
+
+ return dav_push_error(r->pool, status, err->error_id, NULL, err);
+ }
+
err = get_parentpath_resource(r, resource);
if (err)
return err;
]]]