Document Title: =============== Skype v5.3.x v2.2.x v5.2.x - Denial of Service Vulnerability References (Source): ==================== http://www.vulnerability-lab.com/get_content.php?id=181 Release Date: ============= 2011-07-27 Vulnerability Laboratory ID (VL-ID): ==================================== 181 Product & Service Introduction: =============================== Skype is a software application that allows users to make voice and video calls and chats over the Internet. Calls to other users within the Skype service are free, while calls to both traditional landline telephones and mobile phones can be made for a fee using a debit-based user account system. Skype has also become popular for its additional features which include instant messaging, file transfer, and videoconferencing. Skype has 663 million registered users as of 2010. The network is operated by Skype Limited, which has its headquarters in Luxembourg. Most of the development team and 44% of the overall employees of Skype are situated in the offices of Tallinn and Tartu, Estonia. (Copy of the Vendor Homepage: http://en.wikipedia.org/wiki/Skype) Abstract Advisory Information: ============================== Vulnerability-Lab team discovered a local & remote Denial of Service Vulnerability on the Skype v5.3.x v2.2.x v5.2.x Vulnerability Disclosure Timeline: ================================== 2011-07-06: Vendor Notification 2011-07-08: Vendor Response/Feedback 2011-07-20: Vendor Fix/Patch 2011-07-28: Public or Non-Public Disclosure Discovery Status: ================= Published Affected Product(s): ==================== Exploitation Technique: ======================= Remote Severity Level: =============== Medium Technical Details & Description: ================================ A stable denial of service vulnerability is located in the windows version of skype. The Bug is located in the notification module of the Benachrichtigungsoptionen. The vulnerability allows an local attacker to crash the complete skype process via APPHang(application-hang) & APPCrash. The bug allows an local attacker to block the users message board by including on the savebox a %long+[Space]+%long message. The input field of the notifification-option has no size restriction as maximum. After including the software ever asks ifself on every keyboard attempt ... whats inside? The result is in a stable denial of service apphang & appcrash ... also after a restart because its saved. ;) Vulnerable Module(s): [+] Benachrichtigungsoptionen - Word Notification Setting Verified on OS: [+] Windows [+] MacOS [+] Linux Affected OS version(s): Windows v5.3.0.120, 5.4.x, 5.5.x & older versions MacOS v5.2.0.1523 & older versions Ubuntu v2.2.0.35 & older versions Debian v2.2.0.35-1 & older versions Fedora v2.2.0.35-f & older versions Suse v2.2.0.35-s & older versions Picture(s): ../1.png ../2.png ../3.png ../4.png ../5.png ../6.png ../7.png ../8.png Proof of Concept (PoC): ======================= The vulnerability can be exploited by local attackers. For demonstration or reproduce ... Technique(s): => Install => Login => Choose Username => Insert large String => Persistetn Weakness on view of profile or message sending => After insert the vulnerability is exploitable from local techique to remote Manually reproduce ... 1. Install Skype Software 2. Register an Account 3. Login, click on a user in the bar 4. Switch to the Notificationoptions on the skype top menu 5. Check on the last box were "Nur benachrichten wenn wörter geschrieben wurden" is located 6. Implement > %long+[Space]+%long 7. Save the Configuration 8. Now the bug can be exploited via inter action of remote attacker by sending you 1 charakter Analyses: ../AppHang_Skype.exe_2794e078fd2583f9c2d7ba5fcfdd99371f461cb1_01caed60 ../AppHang_Skype.exe_97123e82cc7a24daaf86b37f05b6fe7cb2ac0c5_15c6a1b2 ../AppHang_Skype.exe_ac6288b29d34cbca057010ebc6e75853ea6767_0a087798 ../AppHang_Skype.exe_d3339b31fc3e889da580a3304baee6ec8eaad66_056c3c3c ../AppHang_Skype.exe_d3339b31fc3e889da580a3304baee6ec8eaad66_0367ba7f ../AppHang_Skype.exe_de34bcdc54d51498c88c883af18b128304e38f2_15c45d14 ../skype-debug_access-violation2.txt Solution - Fix & Patch: ======================= 2011-10-**: Vendor Fix/Patch (Fix will be provided soon!) Security Risk: ============== The security risk of the vulnerability is estimated as medium because its a stable software crash without secure exception-handling. Credits & Authors: ================== Vulnerability Research Laboratory - Benjamin Kunz Mejri (Rem0ve) Disclaimer & Information: ========================= The information provided in this advisory is provided as it is without any warranty. Vulnerability-Lab disclaims all warranties, either expressed or implied, including the warranties of merchantability and capability for a particular purpose. Vulnerability- Lab or its suppliers are not liable in any case of damage, including direct, indirect, incidental, consequential loss of business profits or special damages, even if Vulnerability-Lab 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. 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