From mrg@ETERNA.COM.AU Mon May 31 06:28:17 1999 From: matthew green To: BUGTRAQ@netspace.org Date: Fri, 21 May 1999 23:02:25 +1000 Reply-To: tech-security@netbsd.org Subject: NetBSD Security Advisory 1999-010 -----BEGIN PGP SIGNED MESSAGE----- NetBSD Security Advisory 1999-010 ================================= Topic: ARP table vulnerability Version: NetBSD-1.3* Severity: Denial of service or traffic hijacking from local network cable is possible Abstract ======== The implementation of ARP packet reception is vulnerable two attacks: - on multihomed hosts, ARP packets from cable A can overwrite ARP entries for cable B. - for all hosts, ARP packets can overwrite ARP entries marked as static. Technical Details ================= ARP is a protocol used to dynamically obtain IPv4 to Link level address translation, used for Ethernet, FDDI, Token ring, and ARCnet cables, described in RFC 826. The first vulnerability is specific to hosts with more than one ARP capable network attached. The address information of incoming ARP packets is not checked to ensure that it corresponds to one of the addresses of the interface on which the packet arrived. Thus, it would be able to suppress or redirect traffic from the attacked host to a different destination. The second vulnerability is related to so-called "static" arp entries. The original NetBSD ARP implementation (as that of most other vendors) allows the creation of "static" or "permanent" ARP entries. They are typically used for two reasons: - as a security measure, to disallow the redirection of traffic addressed to priviledged hosts by rogue hosts on the cable to themselves or elsewhere, - as a cheap routing protocol ("proxy ARP"), mostly when connecting single hosts through point to point links. To the outside, they occur as if they where on the (e.g.) Ethernet, but traffic destined for them is redirected by the ARP mechanism to the routing host. The 2nd usage doesn't create specific denial of service possibilities as the ARP protocol is insecure in itself. However, if static ARP entries are used to prevent D.O.S. attacks, they need to be protected from overwriting. Solutions and Workarounds ========================= NetBSD-1.4, and NetBSD-1.4_BETA after 1999-05-05, are fixed. A patch is available for NetBSD 1.3.3 to fix this problem. You may find this patch on the NetBSD ftp server: ftp://ftp.NetBSD.ORG/pub/NetBSD/misc/security/patches/19990505-arp NetBSD-current since 19990506 is not vulnerable. Users of NetBSD-current should upgrade to a source tree later than 19990506. Thanks To ========= Both vulnerabilities were reported by Olaf "Rhialto" Seibert in NetBSD PR 7489 and PR 7490. A fix was provided by Zdenek Salvet in PR 7497, and integrated into NetBSD by Ignatios Souvatzis. Revision History ================ 1999/05/21 - initial version More Information ================ Information about NetBSD and NetBSD security can be found at http://www.NetBSD.ORG/ and http://www.NetBSD.ORG/Security/. Copyright 1999, The NetBSD Foundation, Inc. All Rights Reserved. $NetBSD: NetBSD-SA1999-010.txt,v 1.3 1999/05/21 12:47:00 mrg Exp $ -----BEGIN PGP SIGNATURE----- Version: 2.6.3ia Charset: noconv iQCVAwUBN0VV2j5Ru2/4N2IFAQHDLwQAht39y0fw6s9lve+8L+LDaH5LPDHXkj3X YlPtGQAmqKOy/qf8sRbnHYQOm4uxmLpUv5KJznL37o5C8PvA/YZSU5Yq2S7Modkk Po0fxKeacwwf6y4gkT3s6TNOl1W6vxg3P2Ruir6dRbC5FNS4G6PCboa4yUjA0pg2 MSU393S0GV8= =b765 -----END PGP SIGNATURE-----