Vigil@nce: pam-krb5, bypassing authentication
February 2009 by Vigil@nce
SYNTHESIS OF THE VULNERABILITY
When pam-krb5 uses MIT Kerberos, a local attacker can bypass the
authentication.
Gravity: 2/4
Consequences: administrator access/rights
Provenance: user shell
Means of attack: no proof of concept, no attack
Ability of attacker: expert (4/4)
Confidence: confirmed by the editor (5/5)
Diffusion of the vulnerable configuration: high (3/3)
Creation date: 12/02/2009
IMPACTED PRODUCTS
– Debian Linux
– OpenSolaris
– Sun Solaris
– Sun Trusted Solaris
– Unix - plateform
DESCRIPTION OF THE VULNERABILITY
The pam-krb5 module authenticates users with Kerberos.
There are two main Kerberos implementations:
– MIT Kerberos
– Heimdal Kerberos
The MIT implementation provides the krb5_init_secure_context()
function to initialize Kerberos by ignoring environment variables
in suid/sgid mode. The Heimdal implementation automatically
ignores environment variables.
However, when pam-krb5 uses MIT Kerberos, it does not call
krb5_init_secure_context().
A local attacker can therefore use a suid program (such as su or
sudo) calling mod-krb5, with a malicious environment variable
(such as $KRB5_CONFIG), in order to elevate his privileges.
CHARACTERISTICS
Identifiers: 252767, 6799884, BID-33740, CVE-2009-0360, DSA
1721-1, VIGILANCE-VUL-8467
http://vigilance.fr/vulnerability/pam-krb5-bypassing-authentication-8467