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Thu, 16 Nov 2006

8:40 AM - Vulnerability in Firewire

 Here is an advisory that also affects MidnightBSD.  A patch was added to cvs moments ago. 

Kernel Hacking: If i really know, i can hack

GPG KeyID: 5E90CA19

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FreeBSD all versions FireWire IOCTL kernel integer overflow information disclousure 11/15/2006 Notice =================== This bug has been specially discovered for the Month of Kernel Bugs and to the Hackers to Hackers Conference III ( Summary =================== Firewire device is enabled by default in the GENERIC kernel. It defines an IOCTL function which can be malicious called passing a negative buffer lenght value. This value will bypass the lenght check (because the value is negative) and will be used in a copyout operation. Systems Affected =================== FreeBSD all versions NetBSD all versions DragonFly all versions TrustedBSD* all versions Impact =================== This is a kernel bug and the system can be compromised by local users and important system informations can be discloused (basically, a mem dump ;) ) Explanation =================== Firewire interface can be tunned. It provides an ioctl function receiving many parameters that can be changed. The follow is a code fragment from (FreeBSD - dev/firewire/fwdev.c (fw_ioctl function) || DragonFlyBSD bus/firewire/fwdev.c (fw_ioctl function) || NetBSD - dev/ieee1394/fwdev.c (FW_IOCTL function)) file: if (crom_buf->len < len) len = crom_buf->len; else crom_buf->len = len; err = copyout(ptr, crom_buf->ptr, len); We control the crom_buf->len (it's passed as argument to the ioctl function) so, passing it as a negative value will bypass this if statement (our value is minor than the default one). So, our value is used in a copyout function. ptr is defined before this copyout as: if ( fwdev == NULL ) { ... ptr = malloc(CROMSIZE, M_FW, M_WAITOK); ... } else { ptr = (void *)&fwdev->csrrom[0]; ... } This information disclousure lead an attacker dump all the system memory. Solution =================== Attached in this advisory a patch for the FreeBSD 5.5 (it's pretty simple, so, just need to be little changed to the other BSD's) Timelife =================== 11/15/2006 - Advisory Public Disclousure (sorry for the developers, but we are just respecting the Month of Kernel Bugs Timelife) Acknowledgments =================== Filipe Balestra <> and Rodrigo Rubira Branco (BSDaemon) <> for the discovering, analysis and patch. Contact Information =================== You can reach the authors of this advisory by mail or visiting some websites: -> Personal Website of Filipe -> RISE Security Research (Rodrigo is member of the RISE Security Team) -> Personal Website of Rodrigo References =================== -> Actual version of the advisory -> Related issue Disclaimer (taken from teso-team) =================== This advisory does not claim to be complete or to be usable for any purpose. Especially information on the vulnerable systems may be inaccurate or wrong. The supplied exploit is not to be used for malicious purposes, but for educational purposes only. This advisory is free for open distribution in unmodified form.

--- dev/firewire/fwdev.c.orig Fri Oct 13 13:12:49 2006 +++ dev/firewire/fwdev.c Fri Oct 13 13:13:42 2006 @@ -712,7 +712,7 @@ out: else len = fwdev->rommax - CSRROMOFF + 4; } - if (crom_buf->len < len) + if (crom_buf->len < len && crom_buf->len > 0) len = crom_buf->len; else crom_buf->len = len;

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