QNX Neutrino RTOS fontsleuth Command Format String Vulnerability
iDefense Security Advisory 02.07.06 http://www.idefense.com/intelligence/vulnerabilities/display.php?id=380 February 7, 2006
QNX Software Systems Ltd.'s Neutrino RTOS (QNX) is a real-time operating system designed for use in embedded systems. More information is available at:
fontsleuth is a setuid root binary included by default in version 6.3.0 QNX Neutrino RTOS (QNX). It is a utility that tells the Photon font manager where to look for fonts.
Local exploitation of a format string vulnerability in QNX Neutrino RTOS's (QNX) fontsleuth command allows attackers to gain root privileges.
The problem specifically exists in the handling of a string passed as the zeroth argument to the set user id (setuid) binary fontsleuth. The string is ultimately passed to a formatted print function where a format specifier is not supplied. This allows the attacker to use such dangerous format specifiers as %n and %hn to write to arbitrary areas in memory. Using this method, it is possible to overwrite the stored return address or several function pointers, allowing an attacker to seize CPU control and eventually execute arbitrary code under root privileges.
The following debugger dump shows what successful exploitation of this vulnerability looks like at a low level.
Loaded symbols for /usr/qnx630/target/qnx6/x86/lib/libc.so.2
(gdb) x/i $pc 0xb033ec7e <_Putfld+1082>: mov %ax,(%edx) (gdb) i r eax edx eax 0x4142 16706 edx 0x51525354 1364349780
Both EAX and EDX are controlled by the attacker, allowing an overwrite of any location in memory. Furthermore, multiple writes can be achieved by using more than one write format specifier. An attacker can choose to overwrite the saved return address or function pointer and easily gain control of execution.
Successful exploitation provides local attackers with super-user privileges on the affected system. This allows the attacker to have complete control.
iDefense has confirmed the existence of these vulnerabilities in QNX Neutrino RTOS version 6.3.0. Earlier versions are suspected to be susceptible to exploitation as well.
Clear the set user ID or execute bits from the affected binary or remove it entirely.
VI. VENDOR RESPONSE
The vendor has not responded to communication regarding this issue.
VII. CVE INFORMATION
A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.
VIII. DISCLOSURE TIMELINE
12/23/2004 Initial vendor notification 02/07/2006 Public disclosure
iDefense Labs is credited with this discovery.
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X. LEGAL NOTICES
Copyright © 2006 iDefense, Inc.
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