Cisco OpenSSL Implementation Vulnerability
A new vulnerability in the OpenSSL implementation for SSL has been announced on March 17, 2004.
An affected network device running an SSL server based on an affected OpenSSL implementation may be vulnerable to a Denial of Service (DoS) attack. There are workarounds available to mitigate the effects of this vulnerability on Cisco products in the workaround section of this advisory. Cisco is providing fixed software, and recommends that customers upgrade to it when it is available.
The following products have their SSL implementation based on the OpenSSL code and are affected by this vulnerability.
* Cisco IOS 12.1(11)E and later in the 12.1E release train. Only crypto images (56i and k2) are vulnerable for the Cisco 7100 and 7200 Series Routers.
* Cisco IOS 12.2SY release train. Only crypto images (k8, k9 and k91) are vulnerable for the Cisco Catalyst 6500 Series and Cisco 7600 Series Routers.
* Cisco PIX Firewall
* Cisco Firewall Services Module (FWSM) for the Cisco Catalyst 6500 Series and Cisco 7600 Series routers
* Cisco MDS 9000 Series Multilayer Switch
* Cisco Content Service Switch (CSS) 11000 series
* Cisco Global Site Selector (GSS) 4480
* CiscoWorks Common Services (CWCS) version 2.2 and CiscoWorks Common Management Foundation (CMF) version 2.1
* Cisco Access Registrar (CAR)
Secure Sockets Layer (SSL), is a protocol used to encrypt the data transferred over an TCP session. SSL in Cisco products is mainly used by the HyperText Transfer Protocol Secure (HTTPS) web service for which the default TCP port is 443. The affected products, listed above, are only vulnerable if they have the HTTPS service enabled and the access to the service is not limited to trusted hosts or network management workstations.
To check if the HTTPS service is enabled one can do the following:
1. Check the configuration on the device to verify the status of the HTTPS service.
2. Try to connect to the device using a standard web browser that supports SSL using a URL similar to https://ip_address_of_device/.
3. Try and connect to the default HTTPS port, TCP 443, using Telnet. telnet ip_address_of_device 443. If the session connects the service is enabled and accessible.
Testing by the OpenSSL development team has uncovered a null-pointer assignment in the do_change_cipher_spec() function. A remote attacker could perform a carefully crafted SSL/TLS handshake against a server that used the OpenSSL library in such a way as to cause OpenSSL to crash. This crash on many Cisco products would cause the device to reload. Repeated exploitation of this vulnerability would result in a Denial of Service (DoS) attack on the device.
Another flaw was also discovered in the SSL/TLS handshaking code when using Kerberos ciphersuites. A remote attacker could perform a carefully crafted SSL/TLS handshake against a server configured to use Kerberos ciphersuites in such a way as to cause OpenSSL to crash. None of the Cisco OpenSSL implementations are known to use Kerberos ciphersuites and are therefore not affected by this second vulnerability.
A third vulnerability described in the NISCC advisory is a bug in older versions of OpenSSL, versions before 0.9.6d that can also lead to a Denial of Service attack. None of the Cisco OpenSSL implementations are known to be affected by this older OpenSSL issue.
More information on the OpenSSL vulnerability is available at http://www.openssl.org/news/secadv_20040317.txt.
Obtaining Fixed Software:
Cisco is offering free software upgrades to address this vulnerability for all affected customers.
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 http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at the Cisco Connection Online Software Center at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.
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 http://www.cisco.com/tacpage/sw-center. To access the software download URL, you must be a registered user and you must be logged in.
Customers whose Cisco products are provided or maintained through a prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers, should contact that support organization for assistance with obtaining the software upgrade(s).