Trustwave SpiderLabs Security Advisory TWSL2016-021: Plugin authentication by-pass Vulnerability in Microsoft Skype for Mac OS-X Published: 12/12/2016 Version: 1.0 Vendor: Skype/Microsoft Product: Skype for Mac OS-X Version affected: <= 7.35 Product description: Skype is an IP telephony service provider that offers free calling between subscribers and low-cost calling to people who don't use the service. In addition to standard telephone calls, Skype enables file transfers, texting, video chat and videoconferencing. Finding 1: Plugin authentication by-pass *****Credit: Trustwave Spiderlabs Skype for Mac OS-X provides an API to local programs/plugins executing on the local machine, formally known as the Desktop API (previously known as the Skype Public API – Application Programming Interface) which enables third-party applications to communicate with Skype. An authentication by-pass was discovered in the Desktop API offered by Skype for Mac OS-X whereby a local program could by-pass authentication if they identified themselves as a Skype Dashboard widget program. As such, a local program could attach to the Skype Desktop API without informing the user and asking for permission to attach if they utilised a ‘clientAppName’ value of “Skype Dashbd Wdgt Plugin”. For instance, the proof-of-concept code below will initiate the connection process without asking the user for permission for the process to attach: NSDistributedNotificationCenter *defaultCenter = [NSDistributedNotificationCenter defaultCenter]; [defaultCenter postNotificationName:@"SKSkypeAPIAttachRequest" object:(__bridge NSString *) CFSTR("Skype Dashbd Wdgt Plugin")]; Remediation Steps: Upgrade to Skype 7.37(178) for Mac or the latest stable version. Revision History: 10/13/2016 - Vulnerability disclosed to vendor 10/26/2016 - Patch released by vendor 12/12/2016 - Advisory published About Trustwave: Trustwave is the leading provider of on-demand and subscription-based information security and payment card industry compliance management solutions to businesses and government entities throughout the world. For organizations faced with today's challenging data security and compliance environment, Trustwave provides a unique approach with comprehensive solutions that include its flagship TrustKeeper compliance management software and other proprietary security solutions. Trustwave has helped thousands of organizations--ranging from Fortune 500 businesses and large financial institutions to small and medium-sized retailers--manage compliance and secure their network infrastructure, data communications and critical information assets. Trustwave is headquartered in Chicago with offices throughout North America, South America, Europe, Africa, China and Australia. For more information, visit https://www.trustwave.com About Trustwave SpiderLabs: SpiderLabs(R) is the advanced security team at Trustwave focused on application security, incident response, penetration testing, physical security and security research. The team has performed over a thousand incident investigations, thousands of penetration tests and hundreds of application security tests globally. In addition, the SpiderLabs Research team provides intelligence through bleeding-edge research and proof of concept tool development to enhance Trustwave's products and services. https://www.trustwave.com/spiderlabs Disclaimer: The information provided in this advisory is provided "as is" without warranty of any kind. Trustwave disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Trustwave or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Trustwave or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.