CVE-2008-1805 in Skype
Summary
by MITRE
Incomplete blacklist vulnerability in Skype 3.6.0.248, and other versions before 3.8.0.139, allows user-assisted remote attackers to bypass warning dialogs and possibly execute arbitrary code via a file: URI that ends in an executable extension that is not covered by the blacklist.
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Analysis
by VulDB Data Team • 05/31/2025
The vulnerability identified as CVE-2008-1805 represents a critical incomplete blacklist security flaw within Skype versions prior to 3.8.0.139, specifically affecting version 3.6.0.248. This weakness stems from Skype's inadequate filtering mechanism for file:// URI schemes that attempt to execute potentially malicious files through web-based interfaces. The vulnerability operates by exploiting the software's insufficient validation of file extensions within URI strings, creating a pathway for attackers to bypass built-in security warnings that typically protect users from executing unknown or dangerous files.
The technical implementation of this vulnerability involves Skype's failure to maintain a comprehensive blacklist of executable file extensions that could pose security risks when accessed through file:// URIs. When a user encounters a malicious link containing a file:// URI that points to an executable file, the application should display a warning dialog preventing execution. However, due to the incomplete blacklist, certain file extensions that are not explicitly covered by the security filter can bypass these warnings, allowing attackers to execute code on the victim's system without proper user consent or awareness.
This vulnerability has significant operational impact within enterprise and individual security environments, as it enables remote code execution through user-assisted attacks that require minimal social engineering. Attackers can craft malicious web pages or instant messages containing file:// URIs with executable extensions not included in Skype's security filters, such as .bat, .cmd, .scr, or other potentially dangerous file types. The security implications extend beyond simple code execution to include potential system compromise, data exfiltration, and lateral movement within networks where Skype is used as a communication platform.
The vulnerability aligns with CWE-20, which describes improper input validation, and maps to ATT&CK technique T1059.007 for command and scripting interpreter, as it enables attackers to execute commands through malicious file extensions. Organizations using Skype versions before 3.8.0.139 face increased risk of exploitation through phishing campaigns, drive-by downloads, and malicious website content that leverages this flaw. The security gap demonstrates a classic insufficient blacklist implementation pattern where security controls fail to account for all possible threat vectors, creating attack surfaces that can be exploited by adversaries with minimal technical expertise.
Mitigation strategies should prioritize immediate upgrade to Skype version 3.8.0.139 or later, which includes the corrected blacklist implementation. Network administrators should implement additional protective measures such as web content filtering, email security scanning, and endpoint protection solutions that can detect and block malicious file:// URI patterns. Security awareness training for users regarding suspicious links and attachments remains crucial, as the vulnerability requires user interaction to be exploited. Organizations should also consider implementing application whitelisting policies that restrict execution of unauthorized file types, particularly those with executable extensions that could be leveraged through this vulnerability. The fix implemented in subsequent versions demonstrates proper security engineering practices through comprehensive blacklist maintenance and regular security updates to address known attack patterns and emerging threats in the communication software ecosystem.