Date: Fri, 17 Apr 2015 13:23:27 -0400 From: Rich Felker <dalias@...c.org> To: Matt Johnston <matt@....asn.au> Cc: musl@...ts.openwall.com Subject: Re: Re: Security advisory for musl libc - stack-based buffer overflow in ipv6 literal parsing [CVE-2015-1817] On Fri, Apr 17, 2015 at 09:10:08PM +0800, Matt Johnston wrote: > Hi, > > I think Dropbear probably is vulnerable to CVE-2015-1817 > post-authentication. TCP forwarding requests will call > getaddrinfo() > https://secure.ucc.asn.au/hg/dropbear/file/cbd674d63cd4/dbutil.c#l415 > (moved to netio.c in head, and PF_UNSPEC has been fixed to > AF_UNSPEC). Pre-authentication should be OK, only > getnameinfo() is called (if that's enabled). Yes, I agree dropbear is affected. And wow, this is an utter mess. Not only does dropbear fail to drop root before processing forwards; it NEVER drops root at all. The user's session remains running as root for its full lifetime. Aside from being a huge risk, it also allows users to bypass uid-based firewall rules via port forwarding; for example, a rule that forbids normal users from making outgoing connections on port 25 would not be honored. Is there any reason for not performing the setgroups/setgid/setuid immediately after authentication succeeds? Have you looked at whether it would be easy to patch that in? None of this excuses CVE-2015-1817 which was a huge failure on our part, but it seems pretty crazy that dropbear is doing EVERYTHING as root. > musl's network-facing DNS code seems a bit precarious with > pointer arithmetic? Which code are you talking about? There was a previous problem with dn_expand, which is the main function that comes to mind for me, and the code was fixed and heavily reviewed at the time. Are there other areas you're concerned about? Rich
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