CVE-2008-5714 in Qemu
Summary
by MITRE
Off-by-one error in monitor.c in Qemu 0.9.1 might make it easier for remote attackers to guess the VNC password, which is limited to seven characters where eight was intended.
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Analysis
by VulDB Data Team • 08/31/2019
The vulnerability identified as CVE-2008-5714 represents a critical security flaw in the QEMU virtualization software version 0.9.1 that affects the VNC password handling mechanism. This issue stems from an off-by-one error in the monitor.c file, which creates a significant weakness in the authentication system that could be exploited by remote attackers to compromise virtual machine security. The flaw specifically impacts the VNC password validation process where the system incorrectly handles passwords that exceed the intended character limit, creating predictable patterns that reduce the effective entropy of the authentication mechanism.
The technical implementation of this vulnerability occurs due to improper boundary checking in the password validation routine where the software fails to correctly enforce the intended password length constraint. When a VNC password is entered that exceeds the expected seven-character limit, the off-by-one error causes the system to process the eighth character incorrectly, leading to a situation where the password verification routine operates on an incomplete or miscalculated hash value. This miscalculation creates a vulnerability that allows attackers to systematically guess the correct password through reduced search space, as the eighth character's influence on the final authentication result becomes predictable.
From an operational impact perspective, this vulnerability directly undermines the security of virtualized environments that rely on QEMU for hosting virtual machines. Remote attackers who can establish connections to the vulnerable VNC service can exploit this weakness to perform password guessing attacks with significantly reduced computational requirements compared to brute-forcing the full eight-character password space. The vulnerability particularly affects organizations running older QEMU versions where the patch was not yet applied, creating a window of opportunity for malicious actors to gain unauthorized access to virtual machines and potentially escalate their privileges within the virtualized infrastructure.
The flaw aligns with CWE-129, which addresses improper validation of length of input buffers, and demonstrates how seemingly minor coding errors in authentication systems can have substantial security implications. From an attack perspective, this vulnerability maps to several ATT&CK techniques including credential access through password guessing and brute force methods, as well as privilege escalation when attackers can use compromised VNC credentials to gain deeper access to the underlying system. The reduced effective password entropy from seven to six characters significantly decreases the time required for successful password cracking attempts, making this vulnerability particularly dangerous in environments where VNC access is exposed to untrusted networks.
Organizations should immediately implement mitigations including upgrading to patched versions of QEMU where the monitor.c file has been corrected to properly enforce the intended password length validation. Additionally, network segmentation should be implemented to limit direct VNC access from untrusted networks, and alternative authentication mechanisms such as SSH tunneling should be considered for VNC connections. The vulnerability highlights the critical importance of proper input validation in security-sensitive code and demonstrates how even small coding errors can create substantial security risks in virtualization platforms that serve as foundational components of modern IT infrastructure.