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Credit:
The original article can be found at: http://www.cisco.com/en/US/products/products_security_advisory09186a0080b80123.shtml
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Vulnerable Systems:
* Cisco AnyConnect Secure Mobility Client all versions prior to 2.3.185 running on Windows
* Cisco AnyConnect Secure Mobility Client all version in major releases other than 2.5.x running on Linux
* Cisco AnyConnect Secure Mobility Client version in major releases other than 3.0.x. running on Linux
* Cisco AnyConnect Secure Mobility Client version 2.5.x releases prior to 2.5.3041 running on Linux
* Cisco AnyConnect Secure Mobility Client version 3.0.x releases prior to 3.0.629 running on Linux
* Cisco AnyConnect Secure Mobility Client all version in major releases other than 2.5.x running on Apple
* Cisco AnyConnect Secure Mobility Client version in major releases other than 3.0.x. running on Apple
* Cisco AnyConnect Secure Mobility Client version 2.5.x releases prior to 2.5.3041 running on Apple
* Cisco AnyConnect Secure Mobility Client version 3.0.x releases prior to 3.0.629 running on Apple
* Cisco AnyConnect Secure Mobility Client all version in major releases other than 2.5.x running on MacOs
* Cisco AnyConnect Secure Mobility Client version in major releases other than 3.0.x. running on MacOs
* Cisco AnyConnect Secure Mobility Client version 2.5.x releases prior to 2.5.3041 running on MacOs
* Cisco AnyConnect Secure Mobility Client version 3.0.x releases prior to 3.0.629 running on MacOs
* Cisco AnyConnect Secure Mobility Client all versions prior to 2.3.254 running on Windows
Immune Systems:
* Cisco AnyConnect Secure Mobility Client all versions prior to 2.3.254 running on Linux
* Cisco AnyConnect Secure Mobility Client all versions prior to 2.3.254 running on Apple MacOS X
* Cisco AnyConnect Secure Mobility Client for Apple iOS
* IPsec-only Cisco VPN Client
Arbitrary Program Execution Vulnerability
The Cisco AnyConnect Secure Mobility Client can be deployed to remote users from the VPN headend, or it can be installed before the endpoint connects to the VPN headend, a process known as pre-deployment. When the Cisco AnyConnect Secure Mobility Client is pre-deployed, the client software is installed and run like any other application.
When the Cisco AnyConnect Secure Mobility Client is deployed from the VPN headend, an SSL connection is initiated to the VPN headend using a web browser. After the user logs in, the browser displays a portal window and when the user clicks the "Start AnyConnect" link, the process of downloading the Cisco AnyConnect Secure Mobility Client begins. This action causes the browser to first download a "helper" application that aids in downloading and executing the actual Cisco AnyConnect Secure Mobility Client. The helper application is a Java applet on the Linux and MacOS X platforms, and either a Java applet on the Windows platform or an ActiveX control if the browser is capable of utilizing ActiveX controls. The downloaded helper application is executed in the context of the originating site in the user's web browser. The helper application then downloads the Cisco AnyConnect Secure Mobility Client from the VPN headend and executes it.
The helper application fails to properly validate the authenticity of the downloaded Cisco AnyConnect Secure Mobility Client executable when the client is deployed from the VPN headend. An attacker could create a malicious web page that looks like the normal VPN web login page and entice a user, through social engineering or exploitation of other vulnerabilities, to visit it. This would allow the attacker to supply an arbitrary executable that the helper application would download and execute on the machine of the affected user. This arbitrary executable would be executed with the same operating system privileges under which the web browser was run.
Fixed versions of the Cisco AnyConnect Secure Mobility Client use code signing to validate the authenticity of components downloaded from the VPN headend.
This vulnerability is documented in Cisco Bug ID CSCsy00904 ( registered customers only) for Cisco AnyConnect Secure Mobility Client on the Microsoft Windows platform, and in Cisco Bug ID CSCsy05934 ( registered customers only) for Cisco AnyConnect Secure Mobility Client on the Linux and Apple MacOS X platforms. Common Vulnerabilities and Exposures (CVE) IDs CVE-2011-2039 (for CSCsy00904) and CVE-2011-2040 (for CSCsy05934) have been assigned for these vulnerabilities.
Additional Considerations for the Arbitrary Program Execution Vulnerability
Note that while new versions of the ActiveX control and Java applet that are shipped with the Cisco AnyConnect Secure Mobility Client make use of code signing to validate the authenticity of components downloaded from the VPN headend, there is still the issue of old versions that do not validate downloaded components. An attacker may engineer a web page to supply an affected version of the ActiveX control or Java applet and still accomplish arbitrary program execution because of the lack of authenticity validation.
Mitigating the risk of old versions of the ActiveX control can be accomplished in the following ways:
Load fixed Cisco AnyConnect Secure Mobility Client versions on the VPN headend and establish a VPN connection (via web browser or standalone client). This action will cause the new version of the Cisco AnyConnect Secure Mobility Client, including a new version of the ActiveX control to install. When this occurs, an old version of the ActiveX control will not be instantiated if one is presented for download.
Pre-deploy a fixed version of Cisco AnyConnect Secure Mobility Client through enterprise software upgrade infrastructure. This action accomplishes the same result as the previous recommendation -- it deploys new, fixed versions of the ActiveX control so that old, vulnerable versions of the control are not instantiated if one is presented for download.
If deploying the client from the VPN headend is not needed, then the kill bit for the Cisco AnyConnect Secure Mobility Client ActiveX control can be set locally. This action prevents the ActiveX control from being instantiated under any scenario. Instructions for setting the kill bit are beyond the scope of this document; refer to the Microsoft Support article "How to stop an ActiveX control from running in Internet Explorer"at:
http://support.microsoft.com/kb/240797 and the Microsoft Security Vulnerability Research & Defense's "Kill-Bit FAQ" blog posts referenced in the Microsoft Support article for more information.
The CLSID (Class Identifier) for the ActiveX control used by the Cisco AnyConnect Secure Mobility Client is 55963676-2F5E-4BAF-AC28-CF26AA587566, and the ProgID (Program Identifier) is "Cisco.AnyConnect.VPNWeb.1". Note that this CLSID did not change with new versions of the ActiveX control that implement code signing validation.
Mitigating the risk of old versions of the Java applet can be accomplished by blacklisting old, vulnerable versions using the Jar blacklist feature introduced with Java SE 6 Update 14. For information on the Jar blacklist feature refer to the Java SE 6 Update 14 release notes, available at http://www.oracle.com/technetwork/java/javase/6u14-137039.html.
The jar files to be blacklisted are identified by the following SHA-1 message digests:
# 2.3.0254, 2.3.1003, 2.3.2016, 2.4.0202, 2.4.1012,
# 2.5.0217, 2.5.1025, 2.5.2001, 2.5.2006, 2.5.2010,
# 2.5.2011, 2.5.2014, 2.5.2017, 2.5.2018, 2.5.2019
SHA1-Digest-Manifest : xmarT5s8kwnKRLxnCOoLUnxnveE=
# 2.2.0133, 2.2.0136, 2.2.0140
SHA1-Digest-Manifest : 2wXAWNws4uNdCioU1eoCOS4+J3o=
# 2.0.0343, 2.1.0148
SHA1-Digest-Manifest : OlNnvozFCxbJZbRfGiLckOE8uFQ=
Local Privilege Escalation Vulnerability
Unprivileged users can elevate their privileges to those of the LocalSystem account by enabling the Start Before Logon (SBL) feature and interacting with the Cisco AnyConnect Secure Mobility Client graphical user interface in the Windows logon screen.
To prevent this issue, fixed versions of the Cisco AnyConnect Secure Mobility Client limit the amount of interaction that is possible in the client's graphical user interface when it is displayed on the Windows logon screen.
This vulnerability affects only the Cisco AnyConnect Secure Mobility Client for Windows because the SBL feature is not supported by the Linux and MacOS X clients.
CVE Information:
CVE-2011-2039
CVE Information:
CVE-2011-2040
CVE Information:
CVE-2011-2041
Disclosure Timeline:
Revision 1.0 2011-June-01 Initial public release
Revision 1.1 2011-June-06 Updated CVSS score
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