CVE-2018-7225 in LibVNCServer
Summary
by MITRE
An issue was discovered in LibVNCServer through 0.9.11. rfbProcessClientNormalMessage() in rfbserver.c does not sanitize msg.cct.length, leading to access to uninitialized and potentially sensitive data or possibly unspecified other impact (e.g., an integer overflow) via specially crafted VNC packets.
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Analysis
by VulDB Data Team • 02/08/2023
The vulnerability identified as CVE-2018-7225 represents a critical security flaw within LibVNCServer version 0.9.11 and earlier, where the rfbProcessClientNormalMessage function in rfbserver.c fails to properly validate or sanitize the msg.cct.length parameter. This weakness creates a pathway for attackers to manipulate VNC protocol messages and potentially access uninitialized memory regions or sensitive data that may have been previously allocated but not properly cleared. The issue stems from insufficient input validation mechanisms that should have been implemented to ensure message length parameters fall within expected bounds and do not trigger unintended memory access patterns. This vulnerability directly impacts the integrity and confidentiality of VNC server implementations, as it allows for potential data leakage or arbitrary code execution depending on how the uninitialized memory contents are interpreted by the vulnerable system.
The technical exploitation of this vulnerability occurs through crafted VNC packets that manipulate the length field within the client connection type message structure. When the rfbProcessClientNormalMessage function processes these malformed packets, it uses the unsanitized length value to determine memory access boundaries without proper validation checks. This scenario can lead to multiple security implications including information disclosure through uninitialized memory reads, potential integer overflow conditions that could result in memory corruption, or other unspecified behaviors that may be leveraged for further exploitation. The flaw demonstrates poor input sanitization practices that are commonly addressed by established security frameworks and standards. From a CWE perspective, this vulnerability aligns with CWE-129: Improper Validation of Array Index and CWE-704: Incorrect Type Conversion or Cast, as the system fails to validate array indices and properly handle type conversions for message length parameters. The vulnerability also relates to CWE-125: Out-of-bounds Read, as the system may attempt to read memory locations beyond the intended boundaries due to improper length validation.
The operational impact of CVE-2018-7225 extends beyond simple information disclosure, as it represents a potential entry point for attackers seeking to compromise VNC server implementations. Organizations running vulnerable LibVNCServer versions face risks including unauthorized access to desktop environments, potential credential theft through memory analysis, and possible escalation to full system compromise if the uninitialized memory contains sensitive information such as authentication tokens or cryptographic keys. The vulnerability is particularly concerning in environments where VNC servers are exposed to untrusted networks or where they handle sensitive data, as attackers could potentially leverage this flaw to gain access to systems that are otherwise protected by network segmentation or other security controls. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation through memory corruption and credential access through information gathering, as attackers can potentially extract sensitive data from uninitialized memory regions that may contain previously used credentials or session information.
Mitigation strategies for CVE-2018-7225 should focus on immediate patching of affected LibVNCServer installations to version 0.9.12 or later, where the sanitization issues have been addressed. Organizations should also implement network segmentation to limit exposure of VNC servers to untrusted networks and consider deploying additional monitoring solutions to detect anomalous VNC traffic patterns that may indicate exploitation attempts. Security teams should conduct comprehensive vulnerability assessments to identify all systems running affected versions of LibVNCServer and ensure proper input validation mechanisms are in place for all network-facing applications. Additional defensive measures include implementing network access controls that limit VNC server access to authorized users only, deploying intrusion detection systems that can identify malformed VNC packets, and establishing proper incident response procedures for potential exploitation attempts. The vulnerability highlights the importance of robust input validation and memory safety practices in network protocol implementations, emphasizing the need for adherence to security best practices and regular security testing of critical infrastructure components.