Date: Tue, 27 Apr 2010 07:41:15 +0100 From: Steve Langasek <steve.langasek@...onical.com> To: Wouter Coekaerts <coekie@...si.org> Cc: Jamie Strandboge <jamie@...onical.com>, oss-security <oss-security@...ts.openwall.com> Subject: Re: Re: CVE request: irssi 0.8.15 Hi Wouter, Thanks for your mail. On Mon, Apr 26, 2010 at 09:48:29PM +0200, Wouter Coekaerts wrote: > Irssi doesn't have any SSL proxy support. So at first sight, this > seemed like a bugfix for a non-existing feature. Looking at it again, > it seems worse. > There is not much explanation in the linked bug, so I'm making some > assumptions. Correct me if they're wrong. > What you can do in irssi, is configure a proxy, and then attempt to > connect to an SSL IRC server through that proxy. Unfortunately, irssi > currently can't do that, because there is a bug (not a vulnerability) > in irssi that in that case makes it send the configured "proxy_string" > encrypted in SSL instead of in plain text. This misbehaviour could be > used in an akward setup to connect to a proxy that requires SSL, by > pretending to connect to an SSL irc server. To do that you would have > to enable SSL when connecting to the server, even when it's not an SSL > server. By looking at the code, I suspect the patch is about making > that setup work without getting certificate checking errors. Is that > correct? > Because it's more familiar, maybe it's more clear in the webbrowser > equivalent: it is like configuring an http proxy in your browser, > without saying that it requires SSL. Then you surf to > https://example.com, encrypting your connection to the proxy, but > letting the proxy get http://example.com. > It is intended behaviour in irssi that the certificate check fails > here. This patch makes that check pass. That means the proxy is kind > of always doing a MITM attack. The user is given the impression he is > securely connecting to an IRC server, but his actual IRC connection > (between proxy and irc server) is plain text. I would agree with you if IRC proxies were autoconfigured the way web browser proxies often are; in that case, that would clearly be a MITM problem. In *this* case, the IRC proxy I'm connecting to has been painstakingly configured to provide SSL-encrypted proxying to the SSL-enforced IRC servers I use, and modulo this bug where any valid certificate might be substituted for my proxy's certificate, was working entirely as expected. Whether or not irssi "has SSL proxy support", I've been successfully using it with an SSL proxy for several years, precisely as I was intending to use it, with no security vulnerabilities inherent in my setup. To have this stop working in response to a security update is unacceptable collateral damage - my only options then are to stop using a proxy, stop *securing* my proxy with SSL, or to stop using irssi. These are not choices I should have to contend with in response to a security update. -- Steve Langasek Give me a lever long enough and a Free OS Debian Developer to set it on, and I can move the world. Ubuntu Developer http://www.debian.org/ slangasek@...ntu.com vorlon@...ian.org Download attachment "signature.asc" of type "application/pgp-signature" (829 bytes)
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