oss-sec mailing list archives
Re: Attack on badly configured Netfilter-based firewalls
From: Sebastian Krahmer <krahmer () suse de>
Date: Mon, 27 Feb 2012 12:07:10 +0100
Sure, but for 127.0.0.1 it seems the "problem" was big enough to hardcode such a rule in the route input path. For ip6, almost all problems are already re-introduced, and more. cya, Sebastian On Mon, Feb 27, 2012 at 02:01:25PM +0300, ArkanoiD wrote:
It is known "problem" for a long time (note the quotes -- as it is known, it is not a problem anymore and is fixed in all default rulesets). ipv6 may reintorduce it, though. On Mon, Feb 27, 2012 at 11:55:30AM +0100, Sebastian Krahmer wrote:Hi, I know that the 127.0.0.1 trick worked in past, but for loopback addresses this isnt working anymore since quite a while. You will get a 'martian destination', regardless of routing or rp_filter's set. If we talk about a Linux kernel: ip_route_input_slow() { [...] if (ipv4_is_lbcast(daddr) || ipv4_is_zeronet(daddr) || ipv4_is_loopback(daddr)) goto martian_destination; [...] } Or I am doing something seriously wrong. No idea what Solaris or BSD's are doing. For 'real' NIC's this trick is however still working, even if the machine is a host (not a router). This leaves some room for accessing internal admin interfaces from outside. :) However, playing with source addresses to defeat firewalls should be difficult, since most dists enable rp_filter. my 2ct's Sebastian On Mon, Feb 27, 2012 at 01:53:29AM +0400, Solar Designer wrote:On Sun, Feb 26, 2012 at 10:05:55PM +0100, Eric Leblond wrote:On Sun, 2012-02-26 at 12:17 -0700, Kurt Seifried wrote:Are there any helpers that can be abused to open holes in the firewall externally, or is it only internal clients that can cause problems and trigger the firewall to improperly allow network traffic in/out.No, attacker has to be on a network directly connected to the firewall.I guess by "internal clients" Kurt was referring to machines behind the firewall (e.g., someone clicking an URL that has a string looking like an FTP command embedded in it, thereby triggering the FTP helper to open a hole - stuff that was discussed in late 1990s and partially mitigated by hardening the helpers at the time), whereas by "attacker on a network directly connected to the firewall" Eric means that the attacker may be _outside_ the firewall (behind its WAN interface), but on the same network segment (e.g., the attacker might have compromised a nearby server, such as of another customer at a colocation facility). It is known that a machine will generally receive and process a packet routed to one of its NICs by MAC address even if the destination IP address is that of another NIC or even loopback (e.g., it is possible to access services bound to 127.0.0.1 in this way - but only from directly connected machines). Without rp_filter or equivalent, it is possible to have these packets' source addresses match the other NIC's network segment. My _guess_ (based solely on the info posted in here so far) is that the gist of Eric et al.'s new attack is to apply this approach against a protocol helper. The novelty is thus in combining these known things together to arrive at something that to the best of my knowledge has not yet been discussed. I suppose Eric will tell us if this is the correct guess or not. ;-) Alexander-- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer () suse de - SuSE Security Team --- SUSE LINUX Products GmbH, GF: Jeff Hawn, Jennifer Guild, Felix Imend?rffer, HRB 16746 (AG N?rnberg) Maxfeldstra?e 5 90409 N?rnberg Germany email protected and scanned by AdvascanTM - keeping email useful - www.advascan.com
-- ~ perl self.pl ~ $_='print"\$_=\47$_\47;eval"';eval ~ krahmer () suse de - SuSE Security Team --- SUSE LINUX Products GmbH, GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer, HRB 16746 (AG Nürnberg) Maxfeldstraße 5 90409 Nürnberg Germany
Current thread:
- Re: Attack on badly configured Netfilter-based firewalls, (continued)
- Re: Attack on badly configured Netfilter-based firewalls Jussi Eronen (Mar 02)
- Re: Attack on badly configured Netfilter-based firewalls Kurt Seifried (Mar 02)
- Re: Attack on badly configured Netfilter-based firewalls Jussi Eronen (Mar 20)
- Re: Attack on badly configured Netfilter-based firewalls Eric Leblond (Feb 26)
- Re: Attack on badly configured Netfilter-based firewalls Solar Designer (Feb 26)
- Re: Attack on badly configured Netfilter-based firewalls Eric Leblond (Feb 26)
- Re: Attack on badly configured Netfilter-based firewalls yersinia (Feb 27)
- Re: Attack on badly configured Netfilter-based firewalls Sebastian Krahmer (Feb 27)
- Re: Attack on badly configured Netfilter-based firewalls ArkanoiD (Feb 27)
- Re: Attack on badly configured Netfilter-based firewalls Sebastian Krahmer (Feb 27)
- Re: Attack on badly configured Netfilter-based firewalls Eric Leblond (Feb 27)
- Re: Attack on badly configured Netfilter-based firewalls Eric Leblond (Feb 28)