Date: Mon, 30 Oct 2017 21:09:27 +0100 From: Salvatore Bonaccorso <carnil@...ian.org> To: OSS Security Mailinglist <oss-security@...ts.openwall.com> Subject: Quagga: CVE-2017-16227: BGP session termination due to rather long AS paths in update messages Hi The following issue in Quagga got assigned CVE-2017-16227: It was discovered that the bgpd daemon in the Quagga routing suite does not properly calculate the length of multi-segment AS_PATH UPDATE messages, causing bgpd to drop a session and potentially resulting in loss of network connectivity. It was reported as https://bugs.debian.org/879474 in the Debian bugtracker, and following up now here on oss-security. I'm going to fquote the detailed report: > there is a longstanding bug in quagga where certain BGP update messages > cause a quagga bgpd to drop a session, possibly resulting in loss of > network connectivity. > > > Details: > > Long paths in update messages are segmented in BGP, and the bug is in > the recalculation of the framing information if there are more than two > segments. The resulting data is invalid but will will be used for > redistribution. At least if the receiver is another quagga bgpd, that > message is rejected, eventually resulting in a BGP session termination. > > The receiver's log (if written) contains an error message like > | BGP: 172.23.97.181: BGP type 2 length 3074 is too large, attribute total length is 2069. attr_endp is 0x562feb368121. endp is 0x562feb367d2c > then. > > So if a site's BGP peers all run quagga, that site will lose network > connectivity due to frequent session termination. Additionally, the > repeated initial full table transfer will result in a significantly > bigger network load, I've seen around 1 MByte/sec/link, compared to > usually less than one 1 kbyte/sec/link. > > Such extremely long AS paths have occured in the global BGP table at > least four times since June. Last time started on Oct 13th around 20:43 > UTC and lasted until the following week. > > All versions of quagga in Debian are affected. > > > How to fix: > > Kudos to Andreas Jaggi who identified the bug and provided a fix. > After some hours of work I was able to reproduce the issue and can > confirm this patch resolves the issues for all versions of quagga in > Debian (wheezy, jessie, stretch = buster = sid). Details about the > setup available upon request, it's just some stuff to write down. > >  https://lists.quagga.net/pipermail/quagga-dev/2017-September/033284.html > http://git.savannah.gnu.org/cgit/quagga.git/commit/?id=7a42b78be9a4108d98833069a88e6fddb9285008 Regards, Salvatore
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