FreeBSD Kernel i386_set_ldt() Signed nteger Error Lets Local Users Deny Service
SecurityTracker Alert ID: 1016927|
SecurityTracker URL: http://securitytracker.com/id/1016927
(Links to External Site)
Date: Sep 26 2006
Denial of service via local system|
Vendor Confirmed: Yes |
Version(s): 5.5, possibly earlier versions|
iDEFENSE reported a vulnerability in FreeBSD kernel in the i386_set_ldt() function. A local user can cause denial of service conditions.|
A local user can exploit a signed integer flaw to trigger a kernel panic.
The vendor was notified on August 16, 2006.
iDEFENSE reported this vulnerability.
A local user can cause a kernel panic.|
It is unclear if a solution is available.|
The vendor does not plan to issue a security advisory, but may issue Errata Notice.
Vendor URL: www.freebsd.org/security/ (Links to External Site)
Input validation error|
Source Message Contents
Subject: iDefense Security Advisory 09.23.06: FreeBSD i386_set_ldt Integer|
FreeBSD i386_set_ldt Integer Signedness Vulnerability
iDefense Security Advisory 09.23.06
Sep 23, 2006
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
454 sizeof(union descriptor) * i);
As seen on lines 415 and 416, the 'i' and 'largest_ld' variables are
both signed integers. On line 449, uap->start and uap->num are added
together. It should be noted that both of these variables are user
controlled and are not checked properly. On line 452, 'i' can be set to
a negative value which causes the bzero on line 453 to be called with a
very large length parameter. Invalid memory access will result in a
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.
VI. VENDOR RESPONSE
"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
VII. CVE INFORMATION
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
VIII. DISCLOSURE TIMELINE
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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