New RADIUS vulns exposed

[InfoSec News <isn () c4i org>]

http://www.theregister.co.uk/content/5/24298.html

By Thomas C Greene in Washington
Posted: 05/03/2002 at 20:46 GMT

Numerous holes in the ubiquitous RADIUS (remote authentication dial-in
user service) protocol can be exploited with results including denial
of service and running arbitrary code on the target device, a Russian
security researcher has demonstrated. The risk of the DoS attack is
considerably greater, and can be achieved two ways.

First up, according to a bulletin [1] by '3APA3A', during
authentication in several implementations a digest is created
consisting of an initial packet, a message authenticator and a shared
secret concatenated and calculated as an MD5 hash. Unfortunately, the
process doesn't check for adequate space in the target buffer. Thus a
shared secret can be used to overload the buffer, and cause a denial
of service.

If the shared secret were accurately guessed, an attacker could get
privileges on the target RADIUS client or server. While this is far
from a trivial exercise, we note that according to [2] researcher
Joshua Hill, "most client and server implementations only allow shared
secrets to be input as ASCII strings. There are only 94 different
ASCII characters that can be entered from a standard US style keyboard
(out of the 256 possible). Many implementations also restrict the
total length of the shared secret to 16 characters or less. Both of
these restrictions artificially reduce the size of the keyspace that
an attacker must search in order to guess the shared secret."

Next up, still following the 3APA3A bulletin, we have improper
validation of a vendor-specific attribute. Vendor-specific and
user-specific attributes can be passed to the client. If the
vendor-specific header contains less than two bytes, it will be
calculated as a negative number and a denial of service will result.  
It is not necessary to know the shared secret to abuse this flaw.

RADIUS is used widely by ISPs and NSPs for remote user authentication,
so these issues are likely to affect a large number of admins and a
vast heap of equipment and software. It's ubiquitous chiefly because
it's embedded in numerous devices such as routers and switches.

3APA3A has a simple tool for testing RADIUS vulnerabilities available
here [3].

CERT has a bulletin listing all equipment and software presently known
to be vulnerable, along with links to the vendors, posted here [4].


[1] http://www.security.nnov.ru/advisories/radius.asp
[2] http://www.untruth.org/~josh/security/radius/radius-auth.html
[3] http://www.security.nnov.ru/files/test_radius.c
[4] http://www.cert.org/advisories/CA-2002-06.html



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