CVE-2015-8025 in Xscreensaver
Summary
by MITRE
driver/subprocs.c in XScreenSaver before 5.34 does not properly perform an internal consistency check, which allows physically proximate attackers to bypass the lock screen by hot swapping monitors.
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Analysis
by VulDB Data Team • 11/12/2024
The vulnerability identified as CVE-2015-8025 affects the XScreenSaver software version 5.33 and earlier, specifically within the driver/subprocs.c component. This flaw represents a critical security weakness that undermines the fundamental purpose of screen locking mechanisms in graphical desktop environments. The issue stems from insufficient internal consistency validation during monitor configuration changes, creating a window of opportunity for attackers to bypass authentication requirements through physical proximity.
The technical implementation flaw occurs when the XScreenSaver daemon fails to properly validate the consistency of monitor configurations during hot swapping operations. When a user physically connects or disconnects monitors while the system is locked, the software does not adequately verify that the screen locking state remains intact. This oversight allows an attacker to manipulate the display configuration in a manner that temporarily disables or bypasses the lock screen protection. The vulnerability specifically targets the interaction between the screen saver subsystem and the display management components, exploiting a gap in the validation process that should ensure security continuity during hardware changes.
From an operational perspective, this vulnerability creates a significant risk for environments where physical security cannot be guaranteed, particularly in shared or public workspaces. Attackers with physical access to a locked system can exploit this weakness by simply unplugging and replugging display cables, effectively disabling the screen lock without requiring any authentication credentials or specialized tools. The attack vector is particularly concerning because it requires minimal technical knowledge and can be executed quickly, making it a preferred method for unauthorized access in environments where users rely on screen locks for basic security. This vulnerability directly impacts the principle of least privilege and compromises the integrity of the authentication system.
The security implications extend beyond simple unauthorized access, as this vulnerability can serve as a foothold for more sophisticated attacks within a network environment. Once an attacker gains access through this method, they can potentially escalate privileges or conduct reconnaissance activities without raising immediate suspicion. The vulnerability aligns with attack patterns described in the MITRE ATT&CK framework under the technique of privilege escalation through credential access, where attackers exploit system weaknesses to bypass authentication mechanisms. Organizations implementing security controls based on screen lock policies may find their defenses significantly weakened by this flaw.
Mitigation strategies should focus on immediate software updates to XScreenSaver version 5.34 or later, which contains the necessary fixes to address the internal consistency check failure. System administrators should also implement additional monitoring for display configuration changes and consider implementing hardware-level security measures such as cable locks or tamper-evident seals. The fix implemented by the developers addresses the root cause by strengthening the validation process during monitor hot swapping operations, ensuring that the screen locking state remains consistent regardless of display configuration changes. Organizations should also review their security policies to ensure that physical security measures complement digital security controls, as this vulnerability demonstrates the importance of considering all attack vectors including those that exploit physical access opportunities.