CVE-2019-8273 in UltraVNC
Summary
by MITRE
UltraVNC revision 1211 has a heap buffer overflow vulnerability in VNC server code inside file transfer request handler, which can potentially result in code execution. This attack appears to be exploitable via network connectivity. This vulnerability has been fixed in revision 1212.
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Analysis
by VulDB Data Team • 05/29/2020
The vulnerability identified as CVE-2019-8273 represents a critical heap buffer overflow flaw within the UltraVNC remote desktop software version 1211. This issue specifically resides in the VNC server code's file transfer request handler component, making it particularly dangerous as it targets the core functionality of remote desktop access systems. The vulnerability demonstrates a classic memory corruption weakness that can be exploited by remote attackers without requiring local system access or authentication, as the flaw exists within the network-facing server component that handles file transfer operations between client and server systems.
The technical nature of this vulnerability stems from improper bounds checking within the file transfer request handler code, where insufficient validation occurs when processing incoming data buffers. This allows an attacker to provide maliciously crafted input that exceeds the allocated memory buffer size, leading to memory corruption that can be leveraged to execute arbitrary code on the target system. The heap buffer overflow occurs during the processing of file transfer requests, which means that any remote user who can establish a connection to the vulnerable VNC server and initiate a file transfer operation can potentially trigger this vulnerability. The flaw operates at the application layer and requires only network connectivity to be exploited, making it particularly dangerous in environments where VNC servers are accessible over the internet or untrusted networks.
The operational impact of CVE-2019-8273 extends beyond simple remote code execution, as it fundamentally compromises the security posture of systems running vulnerable UltraVNC versions. Attackers who successfully exploit this vulnerability can gain full control over the affected system, potentially leading to data exfiltration, lateral movement within networks, or establishment of persistent backdoors. The vulnerability affects organizations that rely on UltraVNC for remote desktop management, particularly those with exposed VNC servers or those that have not implemented proper network segmentation. The attack vector requires no privileged access or specialized tools beyond basic network connectivity, making it accessible to threat actors with minimal technical expertise.
Organizations should immediately implement mitigation strategies including immediate patching to version 1212 or later, which contains the necessary fixes for this heap buffer overflow vulnerability. Network segmentation and firewall rules should be implemented to restrict access to VNC servers, limiting connections to trusted networks only. Additionally, monitoring should be enhanced to detect unusual file transfer activities that might indicate exploitation attempts. The vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a technique that could be categorized under ATT&CK tactic TA0002 (Execution) and technique T1059.007 (Command and Scripting Interpreter: PowerShell). Security teams should also consider implementing intrusion detection systems to monitor for exploitation attempts and establish incident response procedures specifically addressing remote desktop protocol vulnerabilities. The remediation process should include comprehensive testing of patched systems to ensure that the vulnerability has been properly addressed without introducing new operational issues.