Vulnerability Note VU#943220

MIT KDC vulnerable to double-free when PKINIT enabled

Overview

The KDC in releases krb5-1.7 and later are vulnerable to a double-free vulnerability if they are configured to respond to PKINIT requests.

I. Description

The MIT krb5 Security Advisory 2011-003 states:

"The MIT Kerberos 5 Key Distribution Center (KDC) daemon is vulnerable to a double-free condition if the Public Key Cryptography for Initial Authentication (PKINIT) capability is enabled, resulting in daemon crash or arbitrary code execution (which is believed to be difficult)."

II. Impact

An unauthenticated remote attacker can induce a double-free event, causing the KDC daemon to crash (denial of service), or to execute arbitrary code.

III. Solution

Apply a Patch

Upcoming releases in the krb5-1.7, krb5-1.8, and krb5-1.9 series will contain fixes. In the meantime, apply the following patch:

diff --git a/src/kdc/do_as_req.c b/src/kdc/do_as_req.c
index 46b5fa1..464cb6e 100644
- --- a/src/kdc/do_as_req.c
+++ b/src/kdc/do_as_req.c
@@ -741,6 +741,8 @@ prepare_error_as (struct kdc_request_state *rstate, krb5_kdc_req *request,
                    pad->contents = td[size]->data;
                    pad->length = td[size]->length;
                    pa[size] = pad;
+                    td[size]->data = NULL;
+                    td[size]->length = 0;
                }
            krb5_free_typed_data(kdc_context, td);
        }

Vendor Information

Vendor	Status	Date Notified	Date Updated
MIT Kerberos Development Team	Affected	2011-03-15	2011-03-09

References

http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2011-003.txt
http://web.mit.edu/kerberos/advisories/2011-003-patch.txt
http://web.mit.edu/kerberos/advisories/2011-003-patch.txt.asc

Credit

This issue was discovered by Cameron Meadors of Red Hat.

This document was written by Jared Allar.

Other Information

Date Public:	2011-03-15
Date First Published:	2011-03-15
Date Last Updated:	2011-03-15
CERT Advisory:
CVE-ID(s):	CVE-2011-0284
NVD-ID(s):	CVE-2011-0284
US-CERT Technical Alerts:
Severity Metric:	0.00
Document Revision:	12