Date: Tue, 04 Dec 2012 21:41:54 -0700 From: Kurt Seifried <kseifried@...hat.com> To: oss-security@...ts.openwall.com CC: Greg KH <gregkh@...uxfoundation.org>, kargig@...d.gr Subject: Re: Linux kernel handling of IPv6 temporary addresses -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 11/14/2012 10:14 AM, Greg KH wrote: > On Wed, Nov 14, 2012 at 10:43:22AM +0200, George Kargiotakis > wrote: >> Hello all, >> >> Due to the way the Linux kernel handles the creation of IPv6 >> temporary addresses a malicious LAN user can remotely disable >> them altogether which may lead to privacy violations and >> information disclosure. >> >> By default the Linux kernel uses the 'ipv6.max_addresses' option >> to specify how many IPv6 addresses an interface may have. The >> 'ipv6.regen_max_retry' option specifies how many times the kernel >> will try to create a new address. >> >> Currently, in net/ipv6/addrconf.c,lines 898-910, there is no >> distinction between the events of reaching max_addresses for an >> interface and failing to generate a new address. Upon reaching >> any of the above conditions the following error is emitted by the >> kernel times 'regen_max_retry' (default value 3): >> >> [183.793393] ipv6_create_tempaddr(): retry temporary address >> regeneration [183.793405] ipv6_create_tempaddr(): retry >> temporary address regeneration [183.793411] >> ipv6_create_tempaddr(): retry temporary address regeneration >> >> After 'regen_max_retry' is reached the kernel completely >> disables temporary address generation for that interface. >> >> [183.793413] ipv6_create_tempaddr(): regeneration time exceeded >> - disabled temporary address support >> >> RFC4941 3.3.7 specifies that disabling temp_addresses MUST happen >> upon failure to create non-unique addresses which is not the >> above case. Addresses would have been created if the kernel had a >> higher 'ipv6.max_addresses' limit. >> >> A malicious LAN user can send a limited amount of RA prefixes and >> thus disable IPv6 temporary address creation for any Linux host. >> Recent distributions which enable the IPv6 Privacy extensions by >> default, like Ubuntu 12.04 and 12.10, are vulnerable to such >> attacks. >> >> Due to the kernel's default values for valid (604800) and >> preferred (86400) lifetimes, this scenario may even occur under >> normal usage when a Router sends both a public and a ULA prefix, >> which is not an uncommon scenario for IPv6. 16 addresses are not >> enough with the current default timers when more than 1 prefix is >> advertised. >> >> The kernel should at least differentiate between the two cases >> of reaching max_addresses and being unable to create new >> addresses, due to DAD conflicts for example. > > Have you discussed this with the upstream Linux kernel networking > developers? > > thanks, > > greg k-h Sounds like this needs a CVE, is it correct that: an attacker can create a bunch of RA prefixes thus filling up the # of allowed IPv6 addresses for an interface, preventing any more IPv6 addresses from being assigned to that interface? In other words an attack over the local network resulting in a DoS condition. - -- Kurt Seifried Red Hat Security Response Team (SRT) PGP: 0x5E267993 A90B F995 7350 148F 66BF 7554 160D 4553 5E26 7993 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJQvtCRAAoJEBYNRVNeJnmTlagQAKgjCVHvmGl2fjDLLkK0i37X sI+osD8jJSpyVEezch2moD4d6YpSRzpIULoCms7HQw6JdgGX4U1ArJdWkZd4HVQb Tbj1XdfoKQesLBMXH314565Ui+BJnGo46C01yPltiMlrcsMQtYUqb5HeG1RPUlS1 y9AL0/sVAq/cSUv3X+kHddiDKY7Pwk/kxa59EQ8piKsfHvFAqbgPyWFJldYN2z5C lfdlgxej3ISa+gzYVkp5QAI5NdmmuqmdN8ki3dJwyR1SrWhGMBFV2rJt2IKhA1a7 OfacRZAQqcoE2wQ/4ss+3oYcdVQQUP9ykr3sphL5AjPcOs2B38bwrRt/OIHVMjB5 wl0vCflU9Xwdhv+stw6He6XQw+EXGMxcaguxp0vXOF3ROhLczV6JKCX5GEVJ6IUS Z6bDiWLcq/bj5rkDZRCI/zRCyIEOqVWq2KDECKJ1cM4A4jknCGi9BUtkEFtWBjaq NvF04rTKx+T8ie5nNuj9pXX+h/EsglHKtQu7WRWAI9r+ooCsMUzpweeFF7HhZa1a CMGogVuplgUxqqvwAJ3NjJXGCee6qRpOFC+3o5kZlnlATOP6sqr3y/DjH30pK6k7 y5cM8z8vdxhRfIlTTiCe7JKIEVVuL0sbuMHFytUt8pjpAFUL+3fN9x0BezxwtSxr XNcQ1KEm6ZF8lzSmGY/l =JrA2 -----END PGP SIGNATURE-----
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