Source: cve@mitre.org
Buffer overflow in a certain ActiveX control in SkyFexClient.ocx 1.0.2.77 in SkyFex Client 1.0 allows remote attackers to execute arbitrary code via long strings in the first four arguments to the Start method.
SkyFex Client 1.0 is vulnerable to a critical buffer overflow in its ActiveX control, allowing remote attackers to execute arbitrary code on a victim's system. This vulnerability, triggered by a crafted input to the Start method, can lead to complete system compromise and data theft. Successful exploitation grants attackers full control over the compromised machine.
Step 1: Payload Delivery: The attacker crafts a malicious HTML page or other document containing an embedded instance of the vulnerable SkyFexClient.ocx ActiveX control. This document is then delivered to the victim, typically via phishing, drive-by download, or social engineering.
Step 2: Control Instantiation: The victim's web browser or application attempts to instantiate the vulnerable ActiveX control when the malicious document is opened.
Step 3: Malicious Input: The attacker's crafted document calls the Start method of the SkyFexClient.ocx control, providing excessively long strings as the first four arguments. These long strings contain the attacker's malicious payload, designed to overwrite the stack.
Step 4: Buffer Overflow: The Start method processes the arguments. Due to the lack of input validation, the long strings overflow the allocated buffers.
Step 5: Code Execution: The overflow overwrites the return address on the stack. When the Start method completes, the program jumps to the attacker-controlled address, executing the malicious payload.
The vulnerability stems from a buffer overflow within the SkyFexClient.ocx ActiveX control, specifically in the handling of arguments passed to the Start method. The control fails to properly validate the size of the input strings provided as the first four arguments. This lack of bounds checking allows an attacker to supply excessively long strings, overflowing a fixed-size buffer allocated on the stack. This overflow overwrites adjacent memory, including potentially the return address, enabling the attacker to redirect program execution to malicious code of their choosing. The root cause is a missing or inadequate input validation mechanism, allowing for uncontrolled data to overwrite critical memory regions. The specific function responsible for the overflow is likely within the Start method's argument processing logic.
Due to the age of the vulnerability, it's possible that it has been used by various threat actors, including those focused on espionage and financial gain. Specific APT groups are difficult to attribute definitively without further intelligence. However, the nature of the vulnerability makes it attractive to actors seeking to establish a foothold on a system. This vulnerability is not listed on the CISA KEV.
Network traffic analysis: Look for HTTP requests or other network communications that involve the SkyFex Client. Specifically, examine requests that involve the ActiveX control and its Start method.
File system analysis: Search for the presence of SkyFexClient.ocx (version 1.0.2.77) on the system. Check for suspicious files or modifications to the file.
Process monitoring: Monitor for processes that load SkyFexClient.ocx and analyze their behavior. Look for unusual memory access patterns or code execution.
Registry analysis: Examine the Windows registry for entries related to the SkyFex Client and the ActiveX control. Look for suspicious modifications or entries.
SIEM/IDS rules: Implement rules in your Security Information and Event Management (SIEM) or Intrusion Detection System (IDS) to detect attempts to exploit the vulnerability. These rules should focus on network traffic patterns, file access, and process behavior associated with the exploit.
Uninstall the SkyFex Client 1.0 if it is no longer required. This is the most effective mitigation.
If the SkyFex Client is required, upgrade to a patched version, if one exists. (Unlikely given the age of the software).
Disable ActiveX controls in web browsers or restrict their use to trusted sites only. This can be done through browser settings or Group Policy.
Implement a robust patch management strategy to ensure that all software is up-to-date.
Use a web application firewall (WAF) to filter malicious requests targeting the ActiveX control.
Educate users about the risks of opening suspicious attachments or clicking on untrusted links.
Implement application whitelisting to prevent the execution of unauthorized software, including potentially malicious ActiveX controls.