Multiple vulnerabilities have been reported in Kerberos V5, where the most serious potentially can be exploited by malicious people to compromise a vulnerable system.

1) Various double-free errors within the KDC (Key Distribution Center) cleanup code and in client libraries may allow unauthenticated people to execute arbitrary code on an affected system. The problem is that the ASN.1 decoding functions may free an allocated buffer on the heap, which may then be freed again later by either the KDC cleanup functionality or certain library functions.

This vulnerability affects version 1.3.4 and prior.

2) Some double-free errors within the "krb5_rd_cred()" function may allow authenticated users to execute arbitrary code on an affected system. The problem is that the function attempts to free an allocated buffer on the heap, which has already been freed by the ASN.1 decoding function when an error is encountered.

This can be exploited via affected services calling the vulnerable function (e.g. krshd, klogind, and telnetd).

This vulnerability affects version 1.3.1 and prior.

3) A double-free error within krb524d may allow execution of arbitrary code. The problem is that a buffer allocated on the heap is freed, when conversion of a cross-realm ticket is denied and then later freed again when calling the "krb5_free_ticket()" function.

This vulnerability affects version 1.2.8 through 1.3.4.

4) An error within the ASN.1 decoder when handling indefinite length BER encodings can be exploited by unauthenticated people to cause a vulnerable system to hang in an infinite loop via a specially crafted BER encoding.

This vulnerability affects versions 1.2.2 through 1.3.4.

Solution
Patches are available (see patch matrix in the original advisories).
Further details available to Secunia VIM customers

Provided and/or discovered by
1) Will Fiveash and Nico Williams
2) Joseph Galbraith and John Hawkinson
3) Marc Horowitz
4) Will Fiveash and Nico Williams

Changelog
Further details available to Secunia VIM customers

Original Advisory
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-002-dblfree.txt
http://web.mit.edu/kerberos/www/advisories/MITKRB5-SA-2004-003-asn1.txt

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers