On Fri, Oct 11, 2013 at 8:33 PM, Howard Chu hyc@symas.com wrote:
A paper and presentation making the rounds, claiming to show how webapps using LDAP are vulnerable to search filter spoofing attacks.
http://www.youtube.com/watch?v=wtahzm_R8e4 http://www.blackhat.com/presentations/bh-europe-08/Alonso-Parada/Whitepaper/...
Can't imagine that work like this gets peer-reviewed, because it's mostly garbage. They concoct a scenario in section 4.1.1 of their paper, supposedly showing how filter manipulation can allow a webapp user to bypass LDAP-based authentication. It's ridiculous drivel though, since LDAP-based authentication uses Bind requests and not search filters. Most LDAP deployments don't even give search/compare access to userPassword attributes in the first place.
Just in case anybody out there might be bitten by this info - client-enforced security is no security at all. This is why slapd has such an extensive ACL engine - you enforce access controls on the server, and then it doesn't matter what kind of garbage requests your clients send to you, they can only ever access information that they were allowed to access. This is also why the old pam_ldap authorization scheme was such a bad idea, it relied on the LDAP client (pam_ldap) to correctly implement authorization, instead of the server. (Multiply that by hundreds or thousands of clients and you have an unmanageable, insecurable mess.) This is why we have nssov today.
Of course, this is no excuse to be sloppy when writing your web apps. But if you've configured ACLs to adequately protect your data, then it doesn't matter how sloppy your clients are.
Personally, as a penetration tester, security professional - among other things - I do not agree. O partially.
IMNSHO, the authors have simply traslated in the LDAP world the exactly same problematic that a generic web apps can have regarding SQLI. I do not think they are very different, but LDAP problem in these area are much less popular in the web apps context, probably for reasons of implementation: who like to put some structured information in an LDAP server instead of a relational db? zero or nearly so (I do, because i know LDAP but few others do the same) And I am equally convinced that when there are deficiencies in the webapp input validation the issues are actually the same. Most of the web app are based in carrying out these operations - against the relational or the ldap server - using a webapps user (not the real user), with data access privilege, in general , much broader. For ease of implementation, perhaps. And the ACL serve little in these cases, both in the case of a relational db that of a LDAP server.
Why ? the design of the application is wrong , it does not respect the principle of least privilege. A long time ago i have deployed a web application based on different levels of security privileges: the service users could access the backend LDAP server , but only if the access came from a specific ip address (an application server) and this user can could read some attribute of a specific OU of a specific DIT, others authenticated user could write some specific attribute of a subset of a DIT (and they cannot read other attribute). Using the sophisticated ACL that OPENLDAP offer, different security zone and so on.
How many would do it or do it?
Best Regards and thanks for sharing.
-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/