Software Engineering Institute

The MIT krb5 Kerberos implementation includes a GSS RPC library used in the Kerberos administration server (kadmind). Two flaws exist in the libgssprc library that can cause an array overrun if too many file descriptors are opened. These flaws result in a vulnerability that could allow memory corruption in the kadmind server.

MIT notes that in software versions 1.4 and later, this flaw can only be exploited in configurations that allow large numbers of open file descriptors in a process. In software versions before 1.3, a similar flaw can be exploited in similar circumstances but is further limited to platforms that do not define certain macros in certain C system header files.

An unauthenticated remote attacker can cause memory corruption in the libgssrpc library used by kadmind. kadmind will crash, thereby resulting in a denial of service. MIT notes that it is at least theoretically possible for such corruption to result in database corruption or arbitrary code execution.

Upgrade or apply a patch from the vendor
Patches have been released to address these issues. Please see the Systems Affected section of this document for more details.

Workaround

Before starting kadmind, use "ulimit -n" for Bourne shell and derivatives or "limit descriptors" for C shell and derivatives. Or use similar resource-limiting mechanisms in the invoking process to limit the maximum open file descriptors. The chosen limit should be less than or equal to the value of the FD_SETSIZE macro typically defined in the <sys/select.h> header file.