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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


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