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             AUSCERT External Security Bulletin Redistribution

            ESB-2004.0812 -- Linux kernel IGMP vulnerabilities
                             22 December 2004

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Linux kernel 2.4 version 2.4.28 and prior
                   Linux kernel 2.6 version 2.6.9 and prior
Operating System:  Linux variants
Impact:            Root Compromise
                   Access Confidential Data
                   Denial of Service
Access:            Existing Account
                   Remote/Unauthenticated
CVE Names:         CAN-2004-1137

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PROBLEM:  

	Two vulnerabilities in the IGMP (Internet Group Management Protocol) 
	code in the Linux kernel allow local privillege elevation and remote
	denial of service under conditions described below.

	1. The ip_mc_source() function is part of the user API for IGMP. Due to
	   an incorrectly validated parameter, a program running as an 
	   unprivelleged user is able to overwrite kernel memory.

	2. When an IGMP group query packet is accepted from the network, its 
           contents are not validated properly, allowing a malformed packet to
	   cause remote denial of service.


VERSIONS:

	2.6 kernel versions 2.6.9 and prior are vulnerable.
	2.4 kernel versions 2.4.28 and prior are also vulnerable.
	2.2.x kernels are not vulnerable.


IMPACT:

	1. On SMP systems, this vulnerability allows executing arbitrary code 
	   in kernel mode, allowing root compromise. 

	   On non-SMP systems this is most likely not possible, so the impact
	   is limited to local denial of service.

	   This vulnerability in conjunction with the ip_mc_?sfget() functions 
           also allows reading of blocks of kernel memory, which may contain 
           sensitive information such as passwords.

	2. The second vulnerability allows remote denial of service, if some 
           application on the system is using a multicast socket.
           If the files /proc/net/igmp and /proc/net/mcfilter both exist and
           are non-empty, then the system is vulnerable to this second 
	   vulnerability.

	More information is available in the original advisory. [1]


MITIGATION: 

	No official patch is yet available for this vulnerability. 

	Until a patch is available, AusCERT recommends that system 
        administrators restrict logon access to vulnerable systems, and 
        consider adding a firewall rule to block inbound IGMP packets
	(IP protocol number 2).


REFERENCES:
	
	[1] Linux kernel IGMP vulnerabilities
	    http://isec.pl/vulnerabilities/isec-0018-igmp.txt


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===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
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