CVE-2013-4396 in X.Org Server
Summary
by MITRE
Use-after-free vulnerability in the doImageText function in dix/dixfonts.c in the xorg-server module before 1.14.4 in X.Org X11 allows remote authenticated users to cause a denial of service (daemon crash) or possibly execute arbitrary code via a crafted ImageText request that triggers memory-allocation failure.
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Analysis
by VulDB Data Team • 05/26/2021
The CVE-2013-4396 vulnerability represents a critical use-after-free flaw in the xorg-server module's X.Org X11 implementation that affects versions prior to 1.14.4. This vulnerability exists within the doImageText function located in dix/dixfonts.c, which handles image text operations in the X Window System. The flaw manifests when the server processes crafted ImageText requests from authenticated remote users, creating a dangerous memory management condition that can lead to either daemon crashes or potential arbitrary code execution.
The technical nature of this vulnerability stems from improper memory handling within the font rendering subsystem of X.Org server. When processing ImageText requests, the doImageText function allocates memory for font data structures and subsequently frees this memory without proper validation. An authenticated attacker can craft malicious ImageText requests that trigger specific memory allocation failures, causing the freed memory to be accessed again through use-after-free conditions. This memory corruption pattern creates opportunities for exploitation that can result in system instability or code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable remote code execution on vulnerable systems. The vulnerability affects X.Org X11 servers running versions earlier than 1.14.4, making it particularly concerning for organizations maintaining legacy X11 implementations. The authenticated nature of the attack means that an attacker must first establish a valid connection to the X server, but once authenticated, they can leverage this flaw to compromise system integrity. This vulnerability directly relates to CWE-416, which describes the use of freed memory condition, and can be mapped to ATT&CK technique T1059 for remote code execution through system services.
Systems running affected X.Org server versions are particularly vulnerable because the flaw exists in core font processing functionality that is frequently accessed in graphical environments. The memory allocation failure that triggers this vulnerability occurs during normal operation of the X server when handling font rendering requests, making it difficult to detect and prevent through simple network monitoring. Organizations should prioritize immediate patching of all X.Org server installations to mitigate this risk, as the vulnerability can be exploited remotely by authenticated users without requiring special privileges beyond basic access to the X server. The fix implemented in version 1.14.4 addresses the memory management issues by ensuring proper validation of freed memory references and implementing additional safeguards against malformed ImageText requests that could trigger the use-after-free condition.