Cisco IOS HTTP Server Query Vulnerability
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CIAC INFORMATION BULLETIN
L-012: Cisco IOS HTTP Server Query Vulnerability
October 26, 2000 22:00 GMT
PROBLEM: Cisco had identified a defect in multiple releases of Cisco IOS
software.
PLATFORM: All mainstream Cisco routers and switches running Cisco IOS
software releases 12.0 through 12.1, inclusive.
DAMAGE: If the enable password is known or not set, the defect could be
exploited to produce a denial of service (DoS) attack.
SOLUTION: Until software patches become available, implement appropriate
workaround as indicated by Cisco below.
VULNERABILITY The risk is MEDIUM. This vulnerability may only be exploited if
ASSESSMENT: the enable password is not set, it is well known, or it can be
guessed. The vulnerability is publicly known.
[****** Start of Cisco Bulletin ******]
Cisco IOS HTTP Server Query Vulnerability
Revision 1.0
For public release 2000 October 25 at 08:00 US/Pacific (UTC+0700)
_________________________________________________________________
Summary
A defect in multiple releases of Cisco IOS software will cause a Cisco
router or switch to halt and reload if the IOS HTTP service is
enabled, browsing to
"http://router-ip/anytext?/"
is attempted, and the enable password is supplied when requested. This
defect can be exploited to produce a denial of service (DoS) attack.
The vulnerability, identified as Cisco bug ID CSCdr91706, affects
virtually all mainstream Cisco routers and switches running Cisco IOS
software releases 12.0 through 12.1, inclusive. This is not the same
defect as CSCdr36952.
The vulnerability has been corrected and Cisco is making fixed
releases available for free to replace all affected IOS releases.
Customers are urged to upgrade to releases that are not vulnerable to
this defect as shown in detail below.
This vulnerability can only be exploited if the enable password is
known or not set.
The complete advisory is available at
http://www.cisco.com/warp/public/707/ioshttpserverquery-pub.shtml .
Affected Products
The following products are affected if they run a Cisco IOS software
release that has the defect. To determine if a Cisco product is
running an affected IOS, log in to the device and issue the command
show version. Cisco IOS software will identify itself as "Internetwork
Operating System Software" or "IOS (tm)" software and will display a
version number. Other Cisco devices either will not have the command
show version, or will give different output. Compare the version
number obtained from the router with the versions presented in the
Software Versions and Fixes section below.
Cisco devices that may be running with affected IOS software releases
include:
* Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900,
1000, 1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000,
4500, 4700, AS5200, AS5300, AS5800, 6400, 7000, 7200, ubr7200,
7500, and 12000 series.
* Most recent versions of the LS1010 ATM switch.
* The Catalyst 6000 if it is running IOS.
* The Catalyst 2900XL LAN switch only if it is running IOS.
* The Cisco DistributedDirector.
For some products, the affected software releases are relatively new
and may not be available on every device listed above.
If you are not running Cisco IOS software, you are not affected by
this vulnerability.
Cisco products that do not run Cisco IOS software and are not affected
by this defect include, but are not limited to:
* 700 series dialup routers (750, 760, and 770 series) are not
affected.
* Catalyst 1900, 2800, 2900, 3000, and 5000 series LAN switches are
not affected, except for some versions of the Catalyst 2900XL.
However, optional router modules running Cisco IOS software in
switch backplanes, such as the RSM module for the Catalyst 5000
and 5500, are affected (see the Affected Products section above).
* The Catalyst 6000 is not affected if it is not running IOS.
* WAN switching products in the IGX and BPX lines are not affected.
* The MGX (formerly known as the AXIS shelf) is not affected.
* No host-based software is affected.
* The Cisco PIX Firewall is not affected.
* The Cisco LocalDirector is not affected.
* The Cisco Cache Engine is not affected.
Details
The HTTP server was introduced in IOS release 11.0 to extend router
management to the worldwide Web. The "?" (question mark) character is
defined in the HTML specifications as a delimiter for CGI arguments.
It is also interpreted by the IOS command-line interface as a request
for help.
As of Cisco IOS Software Release 12.0T, the meaning of a question mark
when it appears adjacent to a "/" (slash) character cannot be
determined properly by the URI parser in affected versions of Cisco
IOS software. When a URI containing "?/" is presented to the HTTP
service on the router and a valid enable password is supplied, the
router enters an infinite loop. A watchdog timer expires two minutes
later and forces the router to crash and reload. The router continues
to be vulnerable to this defect as long as it is running an affected
IOS software release and the enable password is known.
This vulnerability may only be exploited if the enable password is not
set, it is well known, or it can be guessed.
In rare cases, an affected device fails to reload, which means an
administrator must physically cycle the power to resume operation.
The HTTP server is not enabled by default except on unconfigured Cisco
model 1003, 1004, and 1005 routers. Once initial access is granted to
configure the router, the customer may set an enable password, and
disable or limit access to the HTTP server by changing the
configuration. Once the new configuration has been saved, the HTTP
server will not be enabled when the router restarts.
Impact
An affected Cisco IOS device that is operating with the HTTP service
enabled and is not protected by having the enable password configured
can be forced to halt for up to two minutes and then reload. The
vulnerability can be exercised repeatedly, possibly creating a denial
of service (DOS) attack, unless the service is disabled, the enable
password is set, or the router is upgraded to a fixed release.
In instances in which a router at a remote location fails to reload,
an administrator must visit the site to enable the device to recover
from the defect.
Software Versions and Fixes
The following table summarizes the Cisco IOS software releases
affected by the defect described in this notice and scheduled dates on
which the earliest corresponding fixed releases will be available.
Dates are tentative and subject to change.
Each table row shows the earliest release that contains the fix in the
"Rebuild", "Interim", or "Maintenance" columns, presented in release
number order.
A Maintenance Release is the most heavily tested and highly
recommended release.
A Rebuild Release is constructed from a previous maintenance or
mainline release and contains a code fix for a specific defect.
Although it receives less testing than a maintenance release, it is
built from a previous maintenance release and includes minimum changes
to address a specific defect.
An Interim Release has much less testing than a maintenance release
and should be selected only if no other suitable release fixes the
defect.
In all cases, customers should exercise caution to be certain the
devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported
properly by the new release.
+==========+=================+==============================================+
| Major | Description or | |
| Release | Platform | Availability of Repaired Releases* |
+==========+=================+===============+==============+===============+
|Unaffected Earlier Releases | Rebuild | Interim** | Maintenance |
+==========+=================+===============+==============+===============+
|11.0 & | | | | |
|earlier, | | |Not | |
|all |Numerous |Not vulnerable |vulnerable |Not vulnerable |
|variants | | | | |
+----------+-----------------+---------------+--------------+---------------+
| |11.1 AA, 11.1 | | | |
|11.1 |CA, 11.1 CC, |Not vulnerable |Not |Not vulnerable |
| |11.1 CT, 11.1 IA | |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
| |11.2 SA, 11.2 | | | |
|11.2 |BC, 11.2 P, 11.2 |Not vulnerable |Not |Not vulnerable |
| |F, 11.2 GS, 11.2 | |vulnerable | |
| |WA3, 11.2 XA | | | |
+----------+-----------------+---------------+--------------+---------------+
| |11.3 NA, 11.3 | | | |
| |AA, 11.3 DA, | | | |
|11.3 |11.3 XA, 11.3 |Not vulnerable |Not |Not vulnerable |
| |HA, 11.3 WA, | |vulnerable | |
| |11.3 MA, 11.3 DB | | | |
+==========+=================+===============+==============+===============+
| 12.0-based Releases | Rebuild | Interim** | Maintenance |
+==========+=================+===============+==============+===============+
| |General | | | |
|12.0 |Deployment (GD): |Not vulnerable |Not |Not vulnerable |
| |all platforms | |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
|12.0DA |xDSL support: |Not vulnerable | Not | Not vulnerable|
| |6100, 6200 | |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
| |Core/ISP | | | |
|12.0S |support: gsr, |Not vulnerable |Not |Not vulnerable |
| |rsp, c7200 | |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
|12.0SC |Cable/broadband | Not |Not |Not vulnerable |
| |ISP: ubr7200 |vulnerable |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
|12.0SL |10000 ESR: c10k |Not vulnerable |Not |Not vulnerable |
| | | |vulnerable | |
+----------+-----------------+---------------+--------------+---------------+
| |Early | | | |
| |Deployment(ED): | | | |
|12.0T |VPN, Distributed | | | |
| |director, | | | |
| |various | | |Unknown |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |cat8510c, | | | |
| |cat8540c, c6msm | | | |
| | | | |12.0(13)W5(19) |
| |ls1010, | | | |
| |cat8510m, | | | |
| |cat8540m | | +---------------+
| |c5atm, c5atm, | | | |
|12.0W5 |c3620, c3640, | | | |
| |c4500, c5rsfc, | | |2000-NOV-13 |
| |c5rsm, c7200, | | | |
| |rsp | | | |
+----------+-----------------+---------------+--------------+---------------+
| |cat2948g, | | |12.0(10)W5(18e)|
| |cat4232 | | +---------------+
| | | | |2000-NOV-14 |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.0XA |(ED): limited | | |12.1(5) |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment |12.1(3a)E4 | | |
|12.0XE |(ED): limited +---------------+ | |
| |platforms |2000-OCT-24 | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment |12.0(4)XH4 | | |
|12.0XH |(ED): limited +---------------+ | |
| |platforms |Unknown | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment |12.0(5)XJ6 | | |
|12.0XJ |(ED): limited +---------------+ | |
| |platforms |Unknown | | |
+==========+=================+===============+==============+===============+
| 12.1-based Releases | Rebuild | Interim** | Maintenance |
+==========+=================+===============+==============+===============+
| |General | | |12.1(05) |
|12.1 |Deployment (GD) | | | |
| |candidate: all | | +---------------+
| |platforms | | |2000-OCT-30 |
+----------+-----------------+---------------+--------------+---------------+
| |Access & Dial |12.1(4)AA1 | | |
| |Early Deployment | | | |
|12.1AA |(ED): c5200, +---------------+ | |
| |c5300, c5800, |Unknown | | |
| |dsc-c5800 | | | |
+----------+-----------------+---------------+--------------+---------------+
| | | | |12.01(04)DA |
|12.1DA |xDSL support: | | | |
| |6160, 6260 | | +---------------+
| | | | |2000-OCT-30 |
+----------+-----------------+---------------+--------------+---------------+
| | | | |12.01(4)DB |
|12.1DB |xDSL support: | | | |
| |c6400 | | +---------------+
| | | | |2000-NOV-13 |
+----------+-----------------+---------------+--------------+---------------+
| | | | |12.01(4)DC |
|12.1DC |xDSL NRP | | | |
| |support: c6400r | | +---------------+
| | | | |2000-NOV-13 |
+----------+-----------------+---------------+--------------+---------------+
| |ELB Early |12.1(3a)E4 | | |
| |Deployment (ED): | | | |
|12.1E |cat6k, 8500, +---------------+ | |
| |ls1010, 7500, |2000-OCT-24 | | |
| |7200, 7100 | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Cable/broadband | 12.01(03a)EC1 | | |
|12.1EC |Early Deployment +---------------+ | |
| |(ED): ubr7200 | Unknown | | |
+----------+-----------------+---------------+--------------+---------------+
| |New technology | | 12.1(5.0.x)T | 12.1(5)T |
|12.1T |Early Deployment | | | |
| |(ED): all | +--------------+---------------+
| |platforms | | Unknown | Unknown |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XA |(ED): limited | Not scheduled | | 12.1(5)T |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XB |(ED): limited | Not scheduled | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| | Early | | | |
| 12.XC |Deployment (ED): |Not scheduled | | 12.1(5)T |
| |limited | | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XD |(ED): limited |Not scheduled | | 12.1(5)T |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XE |(ED): limited |Not scheduled | | 12.1(5)T |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XF |(ED): limited |Not scheduled | | 12.1(5)T |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XG |(ED): limited |Not scheduled | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XH |(ED): limited |Not scheduled | | 12.1(5)T |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XI |(ED): limited |Not scheduled | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XJ |(ED): limited |Not scheduled | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XL |(ED): limited |Not scheduled | | |
| |platforms | | | |
+----------+-----------------+---------------+--------------+---------------+
| |Early Deployment | | | |
|12.1XP |(ED): limited |Not scheduled | | 12.1(5)T |
| |platforms | | | |
+==========+=================+===============+==============+===============+
| Notes |
+===========================================================================+
|* All dates are estimated and subject to change. |
+---------------------------------------------------------------------------+
|** Interim releases are subjected to less rigorous testing than regular |
|maintenance releases, and may have serious bugs. |
+===========================================================================+
Obtaining Fixed Software
Cisco offers free software upgrades to affected customers to remedy
this vulnerability. Customers with service contracts may upgrade to
any software release. Customers without contracts may upgrade only
within a single row of the table above, except that any available
fixed software release will be provided to any customer who can use it
and for whom the standard fixed software release is not yet available.
Customers may install only the feature sets they have purchased.
Not all fixed software may be available as of the release date of this
notice.
Customers with contracts should obtain upgraded software through
regular update channels. Most customers can obtain upgrades via the
Software Center on Cisco's Worldwide Web site at
http://www.cisco.com/.
Customers without contracts should obtain their upgrades by contacting
the Cisco Technical Assistance Center (TAC) as follows:
* +1 800 553 2447 (toll-free call within North America)
* +1 408 526 7209 (toll call from elsewhere in the world)
* E-mail: tac@cisco.com
Additional contact information for the TAC is on-line at
http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml, including
instructions and e-mail addresses for use by non-English speakers.
Give the URL of this notice as evidence of your entitlement to a free
upgrade.
Free upgrades for noncontract customers must be requested through the
TAC.
Please do not contact either "psirt@cisco.com" or
"security-alert@cisco.com" for software upgrades. You will obtain
faster results by contacting the TAC directly.
Workarounds
In lieu of an upgrade, the threat may be eliminated or reduced by
taking any of the following measures:
* Select and configure strong passwords on networking devices.
Or
* Disable the HTTP server using the command no ip http server while
in global configuration mode.
Or
* If the HTTP server must remain enabled while unrepaired, network
access to it can be controlled by applying a standard access list
to the HTTP service itself. For example, if the router's HTTP
service should be reachable only from a browser running on a
computer at IP address 10.1.2.3, then use the following commands
in global configuration mode to create a standard access list and
apply it to the HTTP server:
access-list 1 permit 10.1.2.3
ip http access-class 1
If access list 1 is already in use, then choose another number in
the range 0-99. The implicit deny rule added to the end of every
access list will prevent access from other IP addresses.
Or
* Prevent network access to a vulnerable HTTP server by blocking
traffic in the network path to the server's port with an extended
access list. Such a list would be applied on an interface of the
vulnerable router itself or on another Cisco router in the path of
a potential attack, e.g., applied inbound on the outside interface
of an edge router. The port number used in the extended access
list statement must be the default port used by the HTTP server,
port 80, or equal to whatever value it may have been set via the
ip http port command. Use this workaround with great care; it
cannot be recommended confidently without knowledge of specific
customer network configurations.
Save the resulting configuration in memory so that protection of the
server is not inadvertently removed after a reload.
Exploitation and Public Announcements
The Cisco PSIRT was alerted to this issue by CORE SDI, which
discovered the issue during routine security audits on equipment. The
security audit included a check for common CGI vulnerabilities against
a Cisco device without a configured password; the audit attempted to
browse to "http:///cgi-bin/source-help?/", which caused the
device to crash and reload.
The Cisco PSIRT has received no reports of malicious exploitation of
this vulnerability.
Status of This Notice: INTERIM
This is an interim notice. Cisco expects the contents of this report
to change. The reader is warned that this notice may contain
inaccurate or incomplete information. Although Cisco cannot guarantee
the accuracy of all statements in this notice, all of the facts have
been checked to the best of our ability. Cisco anticipates issuing
monthly updates of this notice until it reaches final status.
Distribution
This notice will be posted at
http://www.cisco.com/warp/public/707/ioshttpserverquery-pub.shtml.
In addition to this HTML version on Cisco's worldwide Web site, a text
version of this notice will be clear-signed with the Cisco PSIRT PGP
key and posted to the following e-mail addresses and Usenet
newsgroups:
* cust-security-announce@cisco.com
* bugtraq@securityfocus.com
* firewalls@lists.gnac.net
* first-teams@first.org (which includes the CERT/CC)
* cisco@spot.colorado.edu
* cisco-nsp@puck.nether.net
* comp.dcom.sys.cisco
* Various internal Cisco mailing lists
Any updates to this notice will appear on Cisco's worldwide Web
server. The updates may or may not be announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check
http://www.cisco.com/warp/public/707/ioshttpserverquery-pub.shtml. for
any updates.
Revision History
+-------------+-----------+---------------------------------------------+
|Revision 1.0 |2000-09-29 |Draft for initial public release 2000-10-11. |
+-------------+-----------+---------------------------------------------+
Cisco Product Security Incident Assistance Process
The Web page at
http://www.cisco.com/warp/public/707/sec_incident_response.shtml
describes how to report security vulnerabilities in Cisco products,
obtain assistance with security incidents, and register to receive
product security information from Cisco Systems, Inc., including
instructions for press inquiries regarding Cisco Security Advisories
and notices. This advisory is Cisco's official public statement
regarding this vulnerability.
_________________________________________________________________
This notice is copyright 2000 by Cisco Systems, Inc. This notice may
be redistributed freely after the release date given at the top of the
text, provided that redistributed copies are complete and unmodified,
including all date and version information.
_________________________________________________________________
[****** End of Cisco Bulletin ******]
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information contained in this bulletin.
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