Software Engineering Institute

A vulnerability exists in the way the krb5_klog_syslog() function used by the Kerberos administration daemon handles specially crafted strings. This vulnerability may cause a buffer overflow that could allow a remote, authenticated user to execute arbitrary code. According to MIT krb5 Security Advisory MITKRB5-SA-2007-002:

krb5_klog_syslog() uses vsprintf() to format text into a fixed-length stack buffer. Format specifiers such as "%s" used in calls to krb5_klog_syslog() may allow formatting of strings of sufficient length to overwrite memory past the end of the stack buffer.

Certain strings received from the client by the kadmin daemon are not truncated prior to logging. Among these strings is the target principal for the kadmin operation.

The KDC truncates most client-originated strings prior to logging. One sort of string which is not truncated is a transited-realms string. A malicious KDC sharing a key with the target realm may issue tickets with specially-crafted transited-realms strings to exploit this vulnerability. There are other places where an authenticated user may cause the KDC to log a string which triggers the vulnerability.

Note that this issue affects all releases of MIT krb5 up to and including krb5-1.6. Other server applications that call the krb5_klog_syslog()function provided with MIT krb5 may also be affected.

This vulnerability can be triggered by sending a specially crafted Kerberos message to a vulnerable system.

A remote, authenticated user may be able to execute arbitrary code on an affected system or cause the affected program to crash, resulting in a denial of service. Secondary impacts of code execution include complete compromise of the Kerberos key database.

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A patch can be obtained from MIT krb5 Security Advisory MITKRB5-SA-2007-002. MIT also states that this will be addressed in the upcoming krb5-1.6.1 release.