Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE-----
===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-2003.0685 -- FreeBSD-SA-03:14.arp [REVISED]
denial of service due to ARP resource starvation
26 September 2003
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Publisher: FreeBSD
Operating System: FreeBSD
BSD
Impact: Denial of Service
Access Required: Remote
Ref: ESB-2003.0682
- --------------------------BEGIN INCLUDED TEXT--------------------
- -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
=============================================================================
FreeBSD-SA-03:14.arp Security Advisory
The FreeBSD Project
Topic: denial of service due to ARP resource starvation
Category: core
Module: sys
Announced: 2003-09-25
Credits: Apple Product Security <product-security@apple.com>
Affects: All releases of FreeBSD
FreeBSD 4-STABLE prior to the correction date
Corrected: 2003-09-24 21:48:00 UTC (RELENG_4, 4.9-PRERELEASE)
2003-09-25 13:33:01 UTC (RELENG_5_1, 5.1-RELEASE-p8)
2003-09-25 13:33:29 UTC (RELENG_5_0, 5.0-RELEASE-p16)
2003-09-25 13:34:14 UTC (RELENG_4_8, 4.8-RELEASE-p10)
2003-09-25 13:34:31 UTC (RELENG_4_7, 4.7-RELEASE-p20)
2003-09-25 13:34:52 UTC (RELENG_4_6, 4.6-RELEASE-p23)
2003-09-25 13:35:18 UTC (RELENG_4_5, 4.5-RELEASE-p34)
2003-09-25 13:35:33 UTC (RELENG_4_4, 4.4-RELEASE-p44)
2003-09-25 13:35:48 UTC (RELENG_4_3, 4.3-RELEASE-p40)
FreeBSD only: NO
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit
<URL:http://www.freebsd.org/security/>.
0. Revision History
v1.0 2003-09-23 Initial release.
v1.1 2003-09-25 Initial patch was incorrect.
I. Background
The Address Resolution Protocol (ARP) is fundamental to the operation
of IP with a variety of network technologies, such as Ethernet and
WLAN. It is used to map IP addresses to MAC addresses, which enables
hosts on a local network segment to communicate with each other
directly. These mappings are stored in the system's ARP cache.
FreeBSD's ARP cache is implemented within the kernel routing table as
a set of routes for the address family in use that have the LLINFO
flag set. This is most commonly often AF_INET (for IPv4). Normally,
when a FreeBSD system receives an ARP request for a network address
configured on one of its interfaces from a system on a local network,
it adds a reciprocal ARP entry to the cache for the system from where
the request originated. Expiry timers are used to purge unused
entries from the ARP cache. A reference count is maintained for each
ARP entry. If the reciprocal ARP entry is not in use by an upper
layer protocol, the reference count will be zero.
II. Problem Description
Under certain circumstances, it is possible for an attacker to flood a
FreeBSD system with spoofed ARP requests, causing resource starvation
which eventually results in a system panic. (The critical condition
is that a route exists for the apparent source of the ARP request.
This is always the case if the system has a default route configured
for that protocol family.)
If a large number of ARP requests with different network protocol
addresses are sent in a small space of time, resource starvation can
result, as the arplookup() function does not delete unnecessary ARP
entries cached as the result of responding to an ARP request.
NOTE WELL: Other BSD-derived systems may also be affected, as the
affected code dates well back to the CSRG branches.
III. Impact
An attacker on the local network may be able to cause the system to
hang or crash. The attacker must have physical access to the shared
network medium. In the case of a wireless network obtaining this
access may be trivial. Networks where proxy ARP is used to direct
traffic between LANs may be particularly vulnerable to the attack,
as the spoofed ARP requests could be bounced through to the target
via routers implementing proxy ARP.
Because the attack operates at Layer 2, the use of strong encryption
technologies such as IPsec cannot protect a system against the attack.
IV. Workaround
There is no known workaround at this time.
V. Solution
Do one of the following:
1) Upgrade your vulnerable system to 4-STABLE; or to the RELENG_5_1,
RELENG_5_0, RELENG_4_8, or RELENG_4_7 security branch dated after the
correction date.
2) To patch your present system:
The following patch has been verified to apply to FreeBSD 5-CURRENT,
4.9-PRERELEASE, and 4.8 systems.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:14/arp.patch
ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-03:14/arp.patch.asc
b) Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Rebuild your kernel as described in
<URL:http://www.freebsd.org/handbook/kernelconfig.html>
and reboot the system.
VI. Correction details
The following list contains the revision numbers of each file that was
corrected in FreeBSD.
Branch Revision
Path
- - -------------------------------------------------------------------------
RELENG_4
src/sys/netinet/if_ether.c 1.64.2.26
RELENG_5_1
src/UPDATING 1.251.2.10
src/sys/conf/newvers.sh 1.50.2.10
src/sys/netinet/if_ether.c 1.104.2.2
RELENG_5_0
src/UPDATING 1.229.2.22
src/sys/conf/newvers.sh 1.48.2.17
src/sys/netinet/if_ether.c 1.96.2.2
RELENG_4_8
src/UPDATING 1.73.2.80.2.12
src/sys/conf/newvers.sh 1.44.2.29.2.11
src/sys/netinet/if_ether.c 1.64.2.22.2.2
RELENG_4_7
src/UPDATING 1.73.2.74.2.23
src/sys/conf/newvers.sh 1.44.2.26.2.22
src/sys/netinet/if_ether.c 1.64.2.19.2.2
RELENG_4_6
src/UPDATING 1.73.2.68.2.52
src/sys/conf/newvers.sh 1.44.2.23.2.40
src/sys/netinet/if_ether.c 1.64.2.18.2.2
RELENG_4_5
src/UPDATING 1.73.2.50.2.51
src/sys/conf/newvers.sh 1.44.2.20.2.35
src/sys/netinet/if_ether.c 1.64.2.15.2.2
RELENG_4_4
src/UPDATING 1.73.2.43.2.52
src/sys/conf/newvers.sh 1.44.2.17.2.43
src/sys/netinet/if_ether.c 1.64.2.11.2.2
RELENG_4_3
src/UPDATING 1.73.2.28.2.39
src/sys/conf/newvers.sh 1.44.2.14.2.29
src/sys/netinet/if_ether.c 1.64.2.10.2.2
- - -------------------------------------------------------------------------
VII. References
<URL:http://docs.info.apple.com/article.html?artnum=61798>
- -----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.3 (FreeBSD)
iD8DBQE/cvNNFdaIBMps37IRAlIsAJ9Kj0u+ZUEOUcpqjl6hISvrALwGQgCfaG5m
jpFBTK86xjFNz4t43ZQtcOU=
=cfvr
- -----END PGP SIGNATURE-----
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
http://www.auscert.org.au/render.html?cid=1980
If you believe that your computer system has been compromised or attacked in
any way, we encourage you to let us know by completing the secure National IT
Incident Reporting Form at:
http://www.auscert.org.au/render.html?it=3192
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business
hours which are GMT+10:00 (AEST). On call after hours
for member emergencies only.
-----BEGIN PGP SIGNATURE-----
Comment: http://www.auscert.org.au/render.html?it=1967
iQCVAwUBP3ON4Sh9+71yA2DNAQFa9AP/RPDQk/ZP9zV1u+jSiI5rQsMre8ftCg4H
/2rDRePMyONb6dRhUqSyCB8SDE6VXdB1VYklLqpnYQmLYm6HdLVfnFZcb4R14bMn
RxekzTqCDCrKW99pJpcpBfvuLU1Hc9b/YLGmk7DXa26OPDQaGdrI6QOJ2jpGn9sV
HA+fkZyVQ64=
=ulKX
-----END PGP SIGNATURE-----