CVE-2005-3265 in Skype
Summary
by MITRE
Buffer overflow in Skype for Windows 1.1.x.0 through 1.4.x.83 allows remote attackers to execute arbitrary code via (1) callto:// and (2) skype:// links, or (3) a non-standard VCARD, possibly due to an underlying error in the SysUtils.WideFmtStr Delphi routine.
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Analysis
by VulDB Data Team • 06/29/2025
The vulnerability identified as CVE-2005-3265 represents a critical buffer overflow flaw within Skype for Windows versions ranging from 1.1.x.0 through 1.4.x.83. This security weakness stems from improper input validation and memory handling within the application's processing of specific URI schemes and contact data formats. The vulnerability specifically affects the SysUtils.WideFmtStr Delphi routine which is responsible for formatting wide character strings, creating an exploitable condition that can be triggered through multiple attack vectors. The buffer overflow occurs when Skype processes maliciously crafted input through the callto:// protocol handler, skype:// protocol handler, or through non-standard VCARD contact files, all of which leverage the underlying vulnerable string formatting function.
The technical exploitation of this vulnerability occurs through the manipulation of input parameters that are processed by the vulnerable SysUtils.WideFmtStr routine. When Skype encounters a malicious callto:// or skype:// link, or a specially crafted VCARD file, the application fails to properly validate the length of input data before copying it into fixed-size buffers. This leads to memory corruption that can be leveraged by remote attackers to overwrite adjacent memory locations, potentially allowing for arbitrary code execution with the privileges of the Skype process. The vulnerability is particularly concerning as it can be triggered through social engineering attacks where users are tricked into clicking malicious links or importing compromised contact files, making it a significant vector for remote code execution attacks.
The operational impact of CVE-2005-3265 extends beyond simple privilege escalation as it provides attackers with a means to gain complete control over affected systems. Since Skype was widely deployed across enterprise and personal networks, the potential for widespread compromise was significant. The vulnerability affects not only individual user systems but also corporate environments where Skype was commonly used for business communications, potentially allowing attackers to establish persistent backdoors or deploy additional malware. The attack vectors are particularly dangerous because they can be executed without requiring user interaction beyond clicking a link or importing a contact file, making the exploitation process relatively straightforward for attackers. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of how improper input validation can lead to remote code execution in client-side applications.
Mitigation strategies for this vulnerability should focus on immediate remediation through official software updates from Skype, as the vendor released patches to address the buffer overflow in subsequent versions. System administrators should implement network-level controls to block or filter potentially malicious URI schemes and contact file imports, particularly in enterprise environments where the risk of targeted attacks is higher. The implementation of application whitelisting policies can help prevent execution of malicious code through compromised Skype installations, while regular security assessments should include verification of Skype version compliance across all endpoints. Additionally, user education regarding the dangers of clicking untrusted links or importing unknown contact files remains crucial in preventing exploitation of this vulnerability. Organizations should consider monitoring network traffic for suspicious callto:// and skype:// protocol usage patterns that may indicate attempted exploitation attempts, aligning with the defensive strategies outlined in the ATT&CK framework for command and control operations.