CVE-2022-23967 in TightVNC
Summary
by MITRE • 01/27/2022
In TightVNC 1.3.10, there is an integer signedness error and resultant heap-based buffer overflow in InitialiseRFBConnection in rfbproto.c (for the vncviewer component). There is no check on the size given to malloc, e.g., -1 is accepted. This allocates a chunk of size zero, which will give a heap pointer. However, one can send 0xffffffff bytes of data, which can have a DoS impact or lead to remote code execution.
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Analysis
by VulDB Data Team • 01/29/2022
The vulnerability identified as CVE-2022-23967 represents a critical security flaw in TightVNC version 1.3.10 affecting the vncviewer component through a heap-based buffer overflow condition. This issue stems from an integer signedness error within the InitialiseRFBConnection function located in the rfbproto.c source file, creating a dangerous scenario where improper input validation leads to memory corruption. The flaw manifests when the application processes connection initialization requests without adequate size validation for memory allocation operations.
The technical implementation of this vulnerability involves a fundamental failure in input sanitization where the system accepts negative integer values, specifically -1, as valid size parameters for malloc operations. When such values are processed, they are interpreted as zero-sized allocations, resulting in heap pointer allocation that appears valid but creates a dangerous memory state. However, the vulnerability extends beyond simple allocation failure as attackers can send 0xffffffff bytes of data, which translates to the maximum unsigned 32-bit integer value, effectively overwhelming the memory management system and creating conditions for exploitation.
The operational impact of this vulnerability spans both denial of service and remote code execution capabilities, making it particularly dangerous for networked environments where TightVNC is deployed. The heap-based buffer overflow creates opportunities for attackers to manipulate memory layout and potentially execute arbitrary code with the privileges of the affected process. This vulnerability directly maps to CWE-190, Integer Overflow or Wraparound, and CWE-122, Heap-based Buffer Overflow, while also aligning with ATT&CK techniques involving privilege escalation and remote code execution through memory corruption exploits.
Mitigation strategies for CVE-2022-23967 should prioritize immediate patching of affected TightVNC installations to version 1.3.11 or later, which includes proper input validation and size checking mechanisms. Network administrators should implement firewall rules to restrict access to VNC ports where possible, while also considering the deployment of intrusion detection systems to monitor for suspicious connection patterns. Additional protective measures include disabling unnecessary VNC services, implementing strong authentication mechanisms, and conducting regular security assessments of remote desktop infrastructure. The vulnerability highlights the importance of proper integer handling in memory allocation functions and demonstrates how seemingly minor input validation gaps can lead to severe security implications. Organizations should also review their remote access policies and ensure that VNC implementations follow security best practices including proper memory management and input sanitization protocols.