CVE-2006-5084 in Skype
Summary
by MITRE
Format string vulnerability in the NSRunAlertPanel function in eBay Skype for Mac 1.5.*.79 and earlier allows remote attackers to cause a denial of service (application crash) and possibly execute arbitrary code via a malformed Skype URL, as originally reported to involve a null dereference.
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Analysis
by VulDB Data Team • 04/23/2026
The vulnerability identified as CVE-2006-5084 represents a critical format string vulnerability within the NSRunAlertPanel function of eBay Skype for Mac versions 1.5.*.79 and earlier. This flaw resides in the application's handling of malformed Skype URLs, which are used to initiate communication sessions within the Skype ecosystem. The vulnerability specifically affects the Mac operating system implementation of the Skype client, creating a potential attack surface that could be exploited by remote threat actors. The issue manifests through improper input validation and processing of URL parameters that are passed to the alert panel function, which is responsible for displaying user interface notifications and prompts.
The technical exploitation of this vulnerability occurs when a maliciously crafted Skype URL is processed by the affected Skype client. The format string vulnerability arises from the application's failure to properly sanitize and validate user-supplied input before passing it to the NSRunAlertPanel function. When the function receives malformed input containing format specifiers, it attempts to interpret these as formatting directives rather than literal text, leading to unpredictable behavior. This misinterpretation can result in memory corruption, stack smashing, or null pointer dereference conditions that ultimately cause the application to crash. The vulnerability's classification as a null dereference indicates that the application attempts to access memory at a null pointer location, which is a common symptom of memory corruption vulnerabilities. According to CWE-134, this vulnerability maps directly to the weakness of using untrusted data in format string contexts, a well-documented security flaw that has been consistently exploited in various software applications.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially enable remote code execution. When the application crashes due to the malformed URL processing, attackers can leverage this instability to inject malicious code into the application's memory space. The crash conditions can be manipulated to overwrite critical memory locations, potentially allowing attackers to redirect execution flow and execute arbitrary code with the privileges of the Skype application. This represents a significant threat to user systems since Skype applications typically have access to network communication capabilities and may be running with elevated privileges. The vulnerability affects the core functionality of the application and could be used in conjunction with other attack vectors to compromise user systems. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving privilege escalation and execution through application input validation flaws, potentially enabling adversaries to establish persistent access through the compromised Skype client.
Mitigation strategies for CVE-2006-5084 must address both immediate remediation and long-term security improvements. The primary solution involves updating to eBay Skype for Mac versions that have patched this vulnerability, specifically versions beyond 1.5.*.79 where the format string handling has been corrected. Organizations should implement network-level controls to block suspicious Skype URL traffic and monitor for unusual patterns in URL processing. Additionally, users should be educated about the risks of clicking untrusted links and the importance of keeping their software updated. The vulnerability highlights the need for proper input validation and sanitization practices, particularly when dealing with user-supplied data in application interfaces. Security professionals should also consider implementing application whitelisting policies that restrict the execution of unauthorized Skype URLs and monitor for anomalous application behavior that might indicate exploitation attempts. Regular security assessments and penetration testing should be conducted to identify similar vulnerabilities in other applications that may be susceptible to format string attacks. The incident underscores the importance of following secure coding practices and adhering to established security guidelines for preventing format string vulnerabilities in software development lifecycle processes.