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Category:   Device (Router/Bridge/Hub)  >   Cisco IOS Vendors:   Cisco
Cisco IOS Bug in Terminating SSL Sessions Lets Remote Users Deny Service
SecurityTracker Alert ID:  1020930
SecurityTracker URL:
CVE Reference:   CVE-2008-3798   (Links to External Site)
Date:  Sep 24 2008
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2, 12.4(17)
Description:   A vulnerability was reported in Cisco IOS in the processing of SSL sessions. A remote user can cause the target device to crash.

A remote user can terminate an SSL session with the target device to cause the target device to crash while processing an SSL packet. The packet is not specially crafted.

Devices running SSL-based services are affected. Services may include:

* HTTP server supporting SSL encryption (HTTPS)
* SSL Virtual Private Network (SSL VPN) also known as AnyConnect VPN
* Open Settlement Protocol (OSP) for Packet Telephony feature

The following releases are affected:

12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2, 12.4(17)

Cisco has assigned Cisco Bug ID CSCsj85065 to this vulnerability.

Impact:   A remote user can cause the target device to crash.
Solution:   The vendor has issued a fix. A patch matrix is available in the vendor's advisory.

The vendor's advisory is available at:

Vendor URL: (Links to External Site)
Cause:   State error

Message History:   None.

 Source Message Contents

Subject:  Cisco Security Advisory: Vulnerability in Cisco IOS While Processing

Hash: SHA1

Cisco Security Advisory: Vulnerability in Cisco IOS While Processing
SSL Packet

Advisory ID: cisco-sa-20080924-ssl

Revision 1.0

For Public Release 2008 September 24 1600 UTC (GMT)

- ---------------------------------------------------------------------


A Cisco IOS device may crash while processing an SSL packet. This can
happen during the termination of an SSL-based session. The offending
packet is not malformed and is normally received as part of the
packet exchange.

Cisco has released free software updates that address this
vulnerability. Aside from disabling affected services, there are no
available workarounds to mitigate an exploit of this vulnerability.

This advisory is posted at

Note: The September 24, 2008 IOS Advisory bundled publication
includes twelve Security Advisories. Eleven of the advisories address
vulnerabilities in Cisco's IOS software, and one advisory addresses
vulnerabilities in Cisco Unified Communications Manager. Each
Advisory lists the releases that correct the vulnerability described
in the Advisory. Please reference the following software table to
find a release that fixes all published IOS software Advisories as of
September 24th, 2008:

Individual publication links are listed below:


Affected Products

Vulnerable Products

Devices running Cisco IOS and using SSL-based services are
susceptible to this vulnerability. Some of the services that utilize
SSL are:

  * HTTP server supporting SSL encryption (HTTPS)
    The following example shows a device that has the standard Cisco
    IOS HTTP server disabled, but the SSL-enabled Cisco IOS HTTP
    server enabled:

        Router#show running-config | include ip http
        no ip http server
        ip http secure-server

  * SSL Virtual Private Network (SSL VPN) also known as AnyConnect
    The following example shows a device that has the SSL VPN feature

        Router#show running-config | include webvpn
        webvpn enable

  * Open Settlement Protocol (OSP) for Packet Telephony feature
    The following example shows a device that has the OSP feature
    enabled and uses HTTPS protocol that is vulnerable:

        Router#show running-config | include url
        url https://<host_ip_address>:443/

The Cisco IOS Bug Toolkit may not accurately reflect the affected
releases for this advisory. The affected releases are as follows:

  * 12.4(16)MR, 12.4(16)MR1, 12.4(16)MR2
  * 12.4(17)

To determine the version of the Cisco IOS software running on a Cisco
product, log in to the device and issue the show version command to
display the system banner. Cisco IOS Software will identify itself as
"Internetwork Operating System Software" or simply "IOS." On the next
line of output, the image name will be displayed between parentheses,
followed by "Version" and the IOS release name. Other Cisco devices
will not have the show version command or will give different output.

    Router#show version
    Cisco IOS Software, 1841 Software (C1841-ADVSECURITYK9-M), Version 12.4(15)T2,
    Technical Support:
    Copyright (c) 1986-2008 by Cisco Systems, Inc.
    Compiled Thu 17-Jan-08 23:12 by prod_rel_team

Additional information about Cisco IOS software release naming is
available at the following link:

Products Confirmed Not Vulnerable

No other Cisco products and Cisco IOS releases are currently known to
be affected by this vulnerability.


This vulnerability is triggered during the termination of an SSL
session. Possession of valid credentials such as a username, password
or a certificate is not required. SSL protocol uses TCP as a
transport protocol. The requirement of the complete TCP 3-way
handshake reduces the probability that this vulnerability will be
exploited through the use of spoofed IP addresses.

A device running vulnerable Cisco IOS Software with SSL-based service
configured will crash while terminating an SSL session.

This vulnerability is documented in Cisco Bug ID CSCsj85065 and has
been assigned Common Vulnerabilities and Exposures (CVE) ID 

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS
scoring in this Security Advisory is done in accordance with CVSS
version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of
the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at

CSCsj85065 - Router reload while processing SSL packets

CVSS Base Score - 7.8

        Access Vector          - Network
        Access Complexity      - Low
        Authentication         - None
        Confidentiality Impact - None
        Integrity Impact       - None
        Availability Impact    - Complete

CVSS Temporal Score - 6.4

        Exploitability          - Functional
        Remediation Level       - Official-Fix
        Report Confidence       - Confirmed


A successful exploit of this vulnerability may cause a crash of the
affected device. Repeated exploitation may result in a sustained
denial of service condition.

Software Versions and Fixes

When considering software upgrades, also consult and any subsequent advisories to 
determine exposure and a complete upgrade solution.

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. If the information is not clear, contact
the Cisco Technical Assistance Center (TAC) or your contracted
maintenance provider for assistance.

Each row of the Cisco IOS software table (below) names a Cisco IOS
release train. If a given release train is vulnerable, then the
earliest possible releases that contain the fix (along with the
anticipated date of availability for each, if applicable) are listed
in the "First Fixed Release" column of the table. The "Recommended
Release" column indicates the releases which have fixes for all the
published vulnerabilities at the time of this Advisory. A device
running a release in the given train that is earlier than the release
in a specific column (less than the First Fixed Release) is known to
be vulnerable. Cisco recommends upgrading to a release equal to or
later than the release in the "Recommended Releases" column of the

|       Major Release       |   Availability of Repaired Releases   |
|    Affected 12.0-Based    |    First Fixed    |    Recommended    |
|         Releases          |      Release      |      Release      |
| There are no affected 12.0 based releases                         |
|    Affected 12.1-Based    |    First Fixed    |    Recommended    |
|         Releases          |      Release      |      Release      |
| There are no affected 12.1 based releases                         |
|    Affected 12.2-Based    |    First Fixed    |    Recommended    |
|         Releases          |      Release      |      Release      |
| There are no affected 12.2 based releases                         |
|    Affected 12.3-Based    |    First Fixed    |    Recommended    |
|         Releases          |      Release      |      Release      |
| There are no affected 12.3 based releases                         |
|    Affected 12.4-Based    |    First Fixed    |    Recommended    |
|         Releases          |      Release      |      Release      |
|                           | 12.4(17a)         |                   |
| 12.4                      |                   | 12.4(18c)         |
|                           | 12.4(18)          |                   |
| 12.4JA                    | Not Vulnerable    |                   |
| 12.4JK                    | Not Vulnerable    |                   |
| 12.4JL                    | Not Vulnerable    |                   |
| 12.4JMA                   | Not Vulnerable    |                   |
| 12.4JMB                   | Not Vulnerable    |                   |
| 12.4JMC                   | Not Vulnerable    |                   |
| 12.4JX                    | Not Vulnerable    |                   |
| 12.4MD                    | Not Vulnerable    |                   |
| 12.4MR                    | 12.4(19)MR        | 12.4(19)MR        |
| 12.4SW                    | Not Vulnerable    |                   |
| 12.4T                     | Not Vulnerable    |                   |
| 12.4XA                    | Not Vulnerable    |                   |
| 12.4XB                    | Not Vulnerable    |                   |
| 12.4XC                    | Not Vulnerable    |                   |
| 12.4XD                    | Not Vulnerable    |                   |
| 12.4XE                    | Not Vulnerable    |                   |
| 12.4XF                    | Not Vulnerable    |                   |
| 12.4XG                    | Not Vulnerable    |                   |
| 12.4XJ                    | Not Vulnerable    |                   |
| 12.4XK                    | Not Vulnerable    |                   |
| 12.4XL                    | Not Vulnerable    |                   |
| 12.4XM                    | Not Vulnerable    |                   |
| 12.4XN                    | Not Vulnerable    |                   |
| 12.4XP                    | Not Vulnerable    |                   |
| 12.4XQ                    | Not Vulnerable    |                   |
| 12.4XT                    | Not Vulnerable    |                   |
| 12.4XV                    | Not Vulnerable    |                   |
| 12.4XW                    | Not Vulnerable    |                   |
| 12.4XY                    | Not Vulnerable    |                   |
| 12.4XZ                    | Not Vulnerable    |                   |


To prevent an exploit of a vulnerable device, SSL-based services need
to be disabled. However, if regular maintenance and operation of the
device relies on this service, there is no workaround.

The following command will disable the vulnerable HTTPS service:

    Router(config)#no ip http secure-server

The following command will disable the vulnerable SSL VPN service:

    Router(config)#no webvpn enable

The following command will disable the vulnerable OSP service:

    Router(config)#no settlement <n>

Another option is to revert to HTTP protocol instead using HTTPS. The
downside of this workaround is that the settlement information will
be sent over the network unprotected.

It is possible to mitigate this vulnerability by preventing
unauthorized hosts from accessing affected devices.

Control Plane Policing (CoPP)

Cisco IOS software versions that support Control Plane Policing
(CoPP) can be configured to help protect the device from attacks that
target the management and control planes. CoPP is available in Cisco
IOS release trains 12.0S, 12.2SX, 12.2S, 12.3T, 12.4, and 12.4T.

In the following CoPP example, the ACL entries that match the exploit
packets with the permit action will be discarded by the policy-map
drop function, whereas packets that match a deny action (not shown)
are not affected by the policy-map drop function:

    !-- Include deny statements up front for any protocols/ports/IP addresses that 
    !-- should not be impacted by CoPP
    !-- Include permit statements for the protocols/ports that will be 
    !-- governed by CoPPaccess-list 100 permit tcp any any eq 443
    !-- Permit (Police or Drop)/Deny (Allow) all other Layer3 and Layer4
    !-- traffic in accordance with existing security policies and
    !-- configurations for traffic that is authorized to be sent
    !-- to infrastructure devices.
    !-- Create a Class-Map for traffic to be policed by
    !-- the CoPP feature.

    class-map match-all drop-SSL-class match access-group 100

    !-- Create a Policy-Map that will be applied to the
    !-- Control-Plane of the device.

    policy-map drop-SSL-policy class drop-SSL-class   drop

    !-- Apply the Policy-Map to the Control-Plane of the
    !-- device.

    control-plane service-policy input drop-SSL-policy

Note: In the preceding CoPP example, the ACL entries with the permit
action that match the exploit packets will result in the discarding
of those packets by the policy-map drop function, whereas packets
that match the deny action are not affected by the policy-map drop

Additional information on the configuration and use of the CoPP
feature is available at the following links:

Access Control List (ACL)

An Access Control List (ACL) can be used to help mitigate attacks
that target this vulnerability. ACLs can specify that only packets
from legitimate sources are permitted to reach a device, and all
others are to be dropped. The following example shows how to allow
legitimate SSL sessions from trusted sources and deny all other SSL

    access-list 101 permit tcp host <legitimate_host_IP_address> host
       <router_IP_address> eq 443
    access-list 101 deny tcp any any eq 443

Obtaining Fixed Software

Cisco has released free software updates that address these
vulnerabilities. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets
they have purchased. By installing, downloading, accessing or
otherwise using such software upgrades, customers agree to be bound
by the terms of Cisco's software license terms found at
or as otherwise set forth at Downloads at

Do not contact or for
software upgrades.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through
their regular update channels. For most customers, this means that
upgrades should be obtained through the Software Center on Cisco's
worldwide website at

Customers using Third Party Support Organizations

Customers whose Cisco products are provided or maintained through
prior or existing agreements with third-party support organizations,
such as Cisco Partners, authorized resellers, or service providers
should contact that support organization for guidance and assistance
with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific
customer situations, such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or
fix is the most appropriate for use in the intended network before it
is deployed.

Customers without Service Contracts

Customers who purchase direct from Cisco but do not hold a Cisco
service contract, and customers who purchase through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should acquire upgrades by contacting the Cisco
Technical Assistance Center (TAC). TAC contacts are as follows.

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
  * e-mail:

Customers should have their product serial number available and be
prepared to give the URL of this notice as evidence of entitlement to
a free upgrade. Free upgrades for non-contract customers must be
requested through the TAC.

Refer to
for additional TAC contact information, including localized telephone
numbers, and instructions and e-mail addresses for use in various

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.

Status of this Notice: FINAL


A stand-alone copy or Paraphrase of the text of this document that
omits the distribution URL in the following section is an
uncontrolled copy, and may lack important information or contain
factual errors.


This advisory is posted on Cisco's worldwide website at:

In addition to worldwide web posting, a text version of this notice
is clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.


Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on
mailing lists or newsgroups. Users concerned about this problem are
encouraged to check the above URL for any updates.

Revision History

| Revision |                   | Initial |
| 1.0      | 2008-September-24 | public  |
|          |                   | release |

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's worldwide website at
This includes instructions for press inquiries regarding Cisco 
security notices. All Cisco security advisories are available at

- ---------------------------------------------------------------------


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