NetBSD LAST_ACK State Transition Bug Lets Remote Users Deny Service
SecurityTracker Alert ID: 1033915|
SecurityTracker URL: http://securitytracker.com/id/1033915
(Links to External Site)
Date: Oct 22 2015
Denial of service via network|
Fix Available: Yes Vendor Confirmed: Yes |
Version(s): 5.1 - 5.1.5, 5.2 - 5.2.3, 6.0 - 6.0.6, 6.1 - 6.1.5|
A vulnerability was reported in NetBSD. A remote user can consume excessive resources on the target system.|
A remote user can establish a TCP connection with the target device and then cause the connection to transition to the LAST_ACK state while the target daemon is not finished sending data to cause the socket to get stuck in the LAST_ACK state. As a result, the remote user can consume memory on the target system.
A remote user can consume excessive memory resources on the target system.|
The vendor has issued a fix.|
The vendor's advisory is available at:
Vendor URL: http://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2015-009.txt.asc (Links to External Site)
Source Message Contents
Subject: NetBSD Security Advisory 2015-009: TCP LAST_ACK state memory exhaustion|
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NetBSD Security Advisory 2015-009
Topic: TCP LAST_ACK state memory exhaustion
Version: NetBSD-current: source prior to Mon, Jul 24th 2015
NetBSD 7.0: not affected
NetBSD 6.1 - 6.1.5: affected
NetBSD 6.0 - 6.0.6: affected
NetBSD 5.2 - 5.2.3: affected
NetBSD 5.1 - 5.1.5: affected
Severity: Potential remote denial of service
Fixed: NetBSD-current: Jul 24th, 2015
NetBSD-7 branch: Jul 24th, 2015
NetBSD-6 branch: Jul 24th, 2015
NetBSD-6-1 branch: Jul 24th, 2015
NetBSD-6-0 branch: Jul 24th, 2015
NetBSD-5 branch: Jul 24th, 2015
NetBSD-5-2 branch: Jul 24th, 2015
NetBSD-5-1 branch Jul 24th, 2015
Please note that NetBSD releases prior to 5.1 are no longer supported.
It is recommended that all users upgrade to a supported release.
TCP sockets that remain in the LAST_ACK state may hold resources
for an unspecified amount of time, which may lead to denial of
service due to memory exhaustion. This vulnerability has been
When closing a connection the TCP socket is entering the LAST_ACK
state in which kernel waits for acknowledgement that FIN was
delivered to the peer or failure of all packet retransmission. In
certain circumstances a socket in this state may hold a significant
amount of memory (mbufs) which can be held for indefinite time,
because the "persist" timer responsible for cleaning up that memory
was previously deactivated. If an attacker is able to make the
attacked systems sockets enter that state, then remote denial of
service is possible due to memory exhaustion.
Solutions and Workarounds
+ Fix from NetBSD autobuild
The fastest way to upgrade to an unaffected kernel, if you are
running or can run a standard kernel built as part of the NetBSD
release process, is to obtain the corresponding kernel from the
daily NetBSD autobuild output and install it on your system.
You can obtain such kernels from http://nyftp.netbsd.org/pub/NetBSD-daily/
where they are sorted by NetBSD branch, date, and architecture. To
fix a system running e.g. NetBSD 6.0 or the stable NetBSD 6.0
branch, the most appropriate kernel will be the "netbsd-6-0" kernel.
To fix a system running NetBSD-current, the "HEAD" kernel should
be used. In all cases, a kernel from an autobuild dated newer than
the fix date for the branch you are using must be used to fix the
+ Fix from source
For all NetBSD versions, if you want to upgrade to a safe kernel
from source, 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.
NEWVERSION with the CVS version of the fix
File versions containing the fix:
FILE HEAD netbsd-7 netbsd-6 netbsd-6-1 netbsd-6-0
+--------------------------- ----- --------- --------- ---------- ----------
src/sys/netinet/tcp_input.c 1.179 1.334.2.2 1.321.2.1 1.321.8.1 1.321.6.1
src/sys/netinet/tcp_output.c 1.184 188.8.131.52 184.108.40.206 220.127.116.11 18.104.22.168
FILE netbsd-5 netbsd-5-2 netbsd-5-1
+--------------------------- ---------- -------------- -------------
src/sys/netinet/tcp_input.c 1.291.4.6 1.222.214.171.124.1 1.2126.96.36.199.1
src/sys/netinet/tcp_output.c 188.8.131.52 184.108.40.206.2.1 220.127.116.11
To update from CVS, re-build, and re-install the kernel:
# cd src
# cvs update -d -P -r NEWVERSION src/sys/netinet/tcp_input.c
# cvs update -d -P -r NEWVERSION src/sys/netinet/tcp_output.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:
Matt Thomas for fixing this issue.
Lawrence Stewart (Netflix, Inc.) and Jonathan Looney (Juniper SIRT) for
reporting this issue.
2015-10-22 Initial release
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/ .
Copyright 2015, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
$Id: NetBSD-SA2015-009.txt,v 1.2 2015/10/22 00:02:31 tonnerre Exp $
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