Bug 648674 (CVE-2010-1324)

Multiple checksum handling vulnerabilities were found in the MIT krb5 GSS-API library:

* krb5 GSS-API applications may accept unkeyed checksums
* krb5 application services may accept unkeyed PAC checksums
* krb5 KDC may accept low-entropy KrbFastArmoredReq checksums

The first flaw can allow an unauthenticated remote attacker to forge GSS tokens that are intended to be integrity-protected but unencrypted, if the targeted pre-existing application session uses a DES session key.

The second flaw can allow an authenticated remote attacker to forge PACs (Privilege Attribute Certificates) if using a KDC that does not filter client-provided PAC data.  This can lead to privilege escalation against a service that relies on PAC contents to make authorization decisions.  This attack will not work in the presence of a MIT krb5 1.8 KDC because the KDC would filter out client-provided PAC authdata.

The final flaw allows a remote unauthenticated attacker to have a 1/256 chance of swapping a client-issued KrbFastReq into a different KDC-REQ, if the armor key is RC4.  The consequences of this issue are believed to be minor.

These flaws affect MIT krb5 version 1.7 and newer.

A patch to correct this flaw, as well the other flaws noted in MITKRB5-SA-2010-007 are available from http://web.mit.edu/kerberos/advisories/2010-007-patch.txt (v1.8) and http://web.mit.edu/kerberos/advisories/2010-007-patch-r17.txt (v1.7).

These issues are collectively known as CVE-2010-1324.  The upstream announcement is available at http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2010-007.txt.


Acknowledgements:

Red Hat would like to thank the MIT Kerberos Team for reporting this issue.