On Fri, Oct 11, 2013 at 8:33 PM, Howard Chu <hyc(a)symas.com>
> A paper and presentation making the rounds, claiming to show how webapps
> using LDAP are vulnerable to search filter spoofing attacks.
> 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.
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.
Nonsense, the issues are nowhere near the same. SQL is a liability because
with injection you can construct any statement of your choosing - Query,
create, modify, or delete information. This liability exists precisely because
SQL is a text-based language.
For an LDAP scenario the window of vulnerability is restricted to a search
filter, only. You cannot use injection to turn an LDAP Search request into a
Modify or Delete request. You cannot destroy or forge data using this "attack"
- it is a much smaller attack surface, and the payoff for an attack is
miniscule. This is a fact - all LDAP-based apps are inherently less vulnerable
than all SQL-based apps, for this simple reason.
And again, with ACLs configured on the server, all any attacker can get is
access to information they were already permitted to see, which completely
closes the window of vulnerability.
Most of the web app
are based in carrying out these operations - against the relational
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
How many would do it or do it?
Look at the volume of messages on this list related to ACLs - clearly, most
OpenLDAP admins are both conscious of and conscientious about using effective
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/