CVE-2012-1699 in X11
Summary
by MITRE
The ProcSetEventMask function in difs/events.c in the xfs font server for X.Org X11R6 through X11R6.6 and XFree86 before 3.3.3 calls the SendErrToClient function with a mask value instead of a pointer, which allows local users to cause a denial of service (memory corruption and crash) or obtain potentially sensitive information from memory via a SetEventMask request that triggers an invalid pointer dereference.
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Analysis
by VulDB Data Team • 01/02/2025
The vulnerability identified as CVE-2012-1699 represents a critical memory management flaw within the xfs font server component of X.Org X11R6 and XFree86 implementations. This issue exists in the ProcSetEventMask function located in difs/events.c, where a fundamental parameter handling error occurs during the processing of SetEventMask requests. The flaw stems from the incorrect passing of a mask value instead of a pointer to the SendErrToClient function, creating a scenario where memory corruption can occur through improper pointer dereferencing operations.
The technical execution of this vulnerability involves local attackers exploiting the improper parameter passing mechanism within the X11 font server's event handling subsystem. When a malicious client sends a SetEventMask request to the xfs server, the server processes this request through the vulnerable ProcSetEventMask function. The function incorrectly treats a mask value as if it were a pointer, leading to an invalid pointer dereference when SendErrToClient is invoked. This error condition can manifest in two primary ways: either causing an immediate system crash through memory corruption or allowing unauthorized information disclosure through memory access violations that may expose sensitive data from the server's memory space.
From an operational impact perspective, this vulnerability creates significant security and stability risks for systems utilizing affected X11 implementations. The potential for denial of service means that legitimate users could be prevented from accessing font services, effectively disrupting graphical applications and desktop environments that depend on proper font rendering. Additionally, the information disclosure aspect poses risks for systems where the memory corruption might expose sensitive data such as authentication tokens, configuration details, or other confidential information stored in the server's memory. The vulnerability affects a broad range of systems including X11R6 through X11R6.6 and XFree86 versions prior to 3.3.3, representing a substantial attack surface across legacy and enterprise environments.
The mitigation strategies for this vulnerability require immediate patching of affected systems with updated X11 server implementations that correct the parameter passing error in the ProcSetEventMask function. System administrators should prioritize updating their X11 font server components to versions that properly handle the mask value as a parameter rather than treating it as a pointer. Network segmentation and access controls should be implemented to limit local access to font servers where possible, reducing the attack surface for local privilege escalation attempts. Security monitoring should be enhanced to detect unusual patterns in SetEventMask request processing that might indicate exploitation attempts. This vulnerability aligns with CWE-466, which addresses the improper handling of pointer dereferences, and maps to ATT&CK technique T1068, which involves exploiting local privileges to gain system access. The vulnerability demonstrates the critical importance of proper parameter validation and memory management in server-side applications, particularly those handling user-provided data through network interfaces.