FreeBSD is a modern operating system for x86, amd64, Alpha, IA-64, PC-98
and SPARC architectures. It's based on the UNIX operating system, BSD,
which was created at the University of California, Berkeley. More
information can be obtained from the FreeBSD Project web site at
Local exploitation of an integer signedness vulnerability in version 5.4
of FreeBSD allows attackers to create a denial of service condition.
The i386_set_ldt() call is provided to allow user-land programs to
dynamically manage the per-process local descriptor table.
Due to the use of signed integers and a lack of proper input validation,
a situation can occur in the kernel where bzero is called with a very
large size parameter. The affected code follows.
415 int error = 0, i; 416 int largest_ld; .. 449 largest_ld = uap->start + uap->num; 450 if (largest_ld > pldt->ldt_len) 451 largest_ld = pldt->ldt_len; 452 i = largest_ld - uap->start; 453 bzero(&((union descriptor *)(pldt->ldt_base))[uap->start], 454 sizeof(union descriptor) * i);As seen on lines 415 and 416, the 'i' and 'largest_ld' variables are
Exploitation of this vulnerability would result in a denial of service
condition on the affected host.
iDefense has confirmed the existence of this problem in FreeBSD 5.5. It
is suspected that versions as early as 5.2 are also affected.
iDefense is not aware of any workarounds for this issue.
"The policy of the FreeBSD Security Team is to not issue security
advisories for local denial of service attacks; since we have not been
able to demonstrate that this bug can result in anything more severe
than a denial of service, we will not be issuing a security advisory
relating to this problem.
It is possible that an Errata Notice will be issued concerning this
The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4178 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
08/16/2006 Initial vendor notification
08/16/2006 Initial vendor response
09/23/2006 Public disclosure
The discoverer of this vulnerability wishes to remain anonymous.
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