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NetBSD Binary Compatibility Code Insufficient Argument Validation
------------------------------------------------------------------------
SUMMARY
Some of NetBSD's functions that implement execution of foreign binaries
are using argument data in an unsafe manner, the implications of which are
ranging from simple DoS against the entire system and even elevation of
privileges.
DETAILS
Vulnerable Systems:
* NetBSD-current: source prior to Oct 27, 2004
* NetBSD version 1.6.x
* NetBSD version 1.5.x
Immune Systems:
* NetBSD current from Oct 28, 2004
* NetBSD version 2.0
* NetBSD version 2.0
* NetBSD version 1.6.3
Kernel syscall implementations must perform appropriate sanity checks on
data passed from userland. The native system calls perform appropriate
checks. However, the compatibility code responsible for execution of
foreign binaries does not.
The issue was originally reported by Evgeny Demidov.
The compat subsystem, in /usr/src/sys/compat/*, allows NetBSD users to run
binaries compiled for other operating systems which run on the same CPU
architecture as the NetBSD host. Typically, the foreign OS supports a set
of system calls which are very similar to NetBSD's. Native instructions do
not need to be translated, but calls to the operating system do.
A binary's native OS is determined at exec() time. The kernel maps the
syscall table for the native OS so that each syscall is delivered to a
foreign OS -> NetBSD translation function, if needed. These translation
functions reorder arguments, reformat them, perform mapping of constants
(such as signal(3) IDs) and call the appropriate native NetBSD system call
to service the application's needs.
Some of the translation functions performed unsafe operations using the
syscall arguments, and were exploitable to cause kernel traps. Some of the
flaws may be exploitable and result in privilege escalation.
All of these attacks require local access to the system. A system with
only trusted user accounts is not immediately at risk. A system running a
custom kernel with all 'options COMPAT_' commented out is not at risk.
Patch Availability:
The NetBSD 2.0 release already includes a fix for this issue. Users of the
1.6 branch are highly encouraged to upgrade to version 1.6.3.
Users of the 1.5 branch which is considered end-of-life are encouraged to
upgrade to a newer version.
ADDITIONAL INFORMATION
The information has been provided by <mailto:security-officer@netbsd.org>
NetBSD Security-Officer.
The original article can be found at:
<http://gleg.net/advisory_netbsd2.shtml>
http://gleg.net/advisory_netbsd2.shtml
The original article can be found at:
<ftp://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2004-010.txt.asc>
ftp://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2004-010.txt.asc
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