NetBSD Security Advisory 2019-004: IPv6 neighbor cache leak on expiration
8 August, 2019 by security-officer@netbsd.org | netbsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 NetBSD Security Advisory 2019-004 ================================= Topic: IPv6 neighbor cache leak on expiration Version: NetBSD-current: affected up to 8.99.51 NetBSD 8.1: affected NetBSD 7.2: not affected NetBSD 7.1.2: not affected NetBSD 7.0.2: not affected Severity: Remote DoS attack can cause the kernel to run out of memory Fixed: NetBSD-current: July 26, 2019 NetBSD-9 branch: not affected NetBSD-8 branch: July 26, 2019 NetBSD-7 branch: not affected NetBSD-7-2 branch: not affected NetBSD-7-1 branch: not affected NetBSD-7-0 branch: not affected Please note that NetBSD releases prior to 7.1 are no longer supported. It is recommended that all users upgrade to a supported release. Abstract ======== An unprivileged user can cause kernel resource exhaustion by creating many IPv6 neighbor entries, because the GC mechanism will not delete them due to a reference counting bug. An explicit cache flush will delete them, recovering the used memory. Technical Details ================= The garbage collection (GC) mechanism of IPv6 neighbor caches has a bug in that it doesn't free expired neighbor caches (llentry) because of a missing refcount decrement. The leak occurs when: 1) giving up a neighbor discovery for a cache, 2) giving up a reachability confirmation for a cache, 3) a cache expires, or 4) a forced GC runs. A forced GC destroys cache entries that have overflowed its limit (ip6.neighborgcthresh). The third and fourth cases can be triggered on receiving NS packets so it can be used as a DoS attack that can originate from machines on the same link. Solutions and Workarounds ========================= For all NetBSD versions, you need to obtain fixed kernel sources, rebuild and install the new kernel, and reboot the system. The fixed source may be obtained from the NetBSD CVS repository. The following instructions briefly summarise how to upgrade your kernel. In these instructions, replace: ARCH with your architecture (from uname -m), and KERNCONF with the name of your kernel configuration file. To update from CVS, re-build, and re-install the kernel: # cd src # cvs update -d -P sys/netinet6/nd6.c # ./build.sh kernel=KERNCONF # mv /netbsd /netbsd.old # cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd # shutdown -r now For more information on how to do this, see: https://www.NetBSD.org/docs/guide/en/chap-kernel.html Thanks To ========= Internet Initiative Japan Inc. for finding and fixing the vulnerability. More Information ================ Advisories may be updated as new information becomes available. The most recent version of this advisory (PGP signed) can be found at https://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2019-004.txt.asc Information about NetBSD and NetBSD security can be found at https://www.NetBSD.org/ https://www.NetBSD.org/Security/ Copyright 2019, The NetBSD Foundation, Inc. All Rights Reserved. Redistribution permitted only in full, unmodified form. $NetBSD: NetBSD-SA2019-004.txt.asc,v 1.1 2019/08/08 10:18:29 christos Exp $ -----BEGIN PGP SIGNATURE----- iQIcBAEBAgAGBQJdS/bCAAoJEIkmHhf170n/ku0P/j/SMhciOSowBzy9L0TX0c+C TIyXqlnOfKWxfoGURIkb0mqEY//lpKXmL6qtXuvtsxgm8xJc9cpEa/yk9qzBtTiw U7yRXCN5Wqv1+Xsh2uun0qMIYesSiTwRrgnoTqLgWvRDIdzOBsyv9BkAf8FCsKhc RMon+BTvAmVTDkKFJgxUQYkgWYjuArnkkhGw789EzRbNAdCbWeoPkEksfeRG3VDC tbtj4FMvuM40XayXhfSia3F+/GvC5bvVx87tkQXCiPum6/dOuTS6GMvqX4fASIPO /27kPVY19OJxmLWR7M1emsxTq7PTV36eOkFDA3RZY5iSZ22YJVcy8zfZTVkHv3wJ FD0buTV8xms6oxw6o9A9TUocaOtVzY7+iExg12do2c4URDxuaX6qer160UlHvxBs mMPStRIJq+2uczMmwFsrLNzl6nad70fv/i//e3MVX5HC/1wk9aTaJIPDH40cU/5Z pd+PvI4veq6ZefkPatiCBKrBTCQkOUMNMQETp7CuF9L49J3QZHV9xFZjtl3F96pk f/AnJuLEn/XZ/kM1dQMItm9w5i9fGnaeQFQ6+sC5VvKxMMVgPFWFCGZa7xAqvP5o ZX3O9tSkSTp2yDWl9SoLDKzpmjK6fkx3IDdxQeH7xpXDvpNl+l+HXUcYS7HJGvPd XhgPZFVcLgSxbl58lWgI =HQQm -----END PGP SIGNATURE-----