CVE-2023-27830 in TightVNC
Summary
by MITRE • 04/12/2023
TightVNC before v2.8.75 allows attackers to escalate privileges on the host operating system via replacing legitimate files with crafted files when executing a file transfer. This is due to the fact that TightVNC runs in the backend as a high-privileges account.
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Analysis
by VulDB Data Team • 11/25/2025
CVE-2023-27830 represents a critical privilege escalation vulnerability affecting TightVNC versions prior to v2.8.75. This vulnerability stems from the insecure handling of file transfer operations within the VNC server implementation, creating a path for attackers to execute malicious code with elevated privileges. The flaw specifically exploits the design decision where TightVNC operates with high-privilege account credentials in the background, making it an attractive target for attackers seeking to leverage existing administrative access for more extensive system compromise.
The technical exploitation occurs during file transfer operations when TightVNC allows attackers to replace legitimate system files with maliciously crafted alternatives. This vulnerability is classified under CWE-276 as improper file permissions and falls into the broader category of privilege escalation flaws that enable attackers to gain elevated system access. The vulnerability exists because TightVNC does not properly validate or sanitize file paths during transfer operations, allowing attackers to manipulate the file system in ways that would normally be restricted to privileged processes. When a file transfer is initiated, the application does not adequately verify the integrity of the destination files or validate that the transfer occurs within appropriate security boundaries.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass potential full system compromise. Attackers who gain initial access through TightVNC can leverage this flaw to install persistent backdoors, modify critical system files, or escalate their access to administrative privileges without requiring additional authentication. This vulnerability is particularly concerning in enterprise environments where VNC servers are commonly deployed for remote administration and support. The attack vector is relatively straightforward as it requires only that an attacker establish a valid VNC session and initiate a file transfer operation, making it accessible to adversaries with basic network access.
Security professionals should implement immediate mitigations including upgrading to TightVNC version 2.8.75 or later, which addresses this privilege escalation issue through improved file handling and validation mechanisms. Additionally, organizations should consider implementing network segmentation to limit access to VNC services, enforcing strong authentication controls, and monitoring for suspicious file transfer activities. The vulnerability aligns with ATT&CK technique T1078 which covers valid accounts and T1543 which covers create or modify system process, making it a significant concern for defensive teams implementing MITRE ATT&CK-based threat models. Organizations should also consider implementing file integrity monitoring solutions to detect unauthorized file modifications that could indicate exploitation of this vulnerability.