CVE-2013-1991 in libXxf86dga
Summary
by MITRE
Multiple integer overflows in X.org libXxf86dga 1.1.3 and earlier allow X servers to trigger allocation of insufficient memory and a buffer overflow via vectors related to the (1) XDGAQueryModes and (2) XDGASetMode functions.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability identified as CVE-2013-1991 resides within the X.org libXxf86dga library version 1.1.3 and earlier, representing a critical security flaw that affects X Window System implementations. This vulnerability specifically targets the XDGAQueryModes and XDGASetMode functions, which are integral components of the XFree86 DGA (Direct Graphics Access) extension used for direct hardware access in graphics environments. The flaw manifests as integer overflows that occur during the processing of graphics mode queries and mode setting operations, creating a pathway for malicious X servers to manipulate memory allocation parameters. These integer overflows are particularly dangerous because they can be exploited to cause memory allocation failures that result in insufficient buffer sizing, ultimately leading to buffer overflow conditions that compromise system stability and security.
The technical implementation of this vulnerability involves the manipulation of integer values within the graphics mode handling functions where input parameters are not properly validated before being used in memory allocation calculations. When an X server processes a request to query or set graphics modes, the library performs calculations based on user-supplied parameters that determine buffer sizes for memory allocation. The integer overflow occurs when these calculations exceed the maximum representable value for the integer type, causing the resulting value to wrap around to a much smaller number. This wrapped value then gets used to allocate memory, creating a situation where insufficient memory is allocated for the actual data that needs to be stored, leading to buffer overflows when the system attempts to write beyond the allocated boundaries.
The operational impact of CVE-2013-1991 extends beyond simple system instability, presenting significant security risks that align with multiple ATT&CK techniques including privilege escalation and denial of service. An attacker leveraging this vulnerability can potentially execute arbitrary code within the context of the X server process, which typically runs with elevated privileges in graphical environments. The vulnerability falls under CWE-190, Integer Overflow or Wraparound, and specifically relates to CWE-129, Improper Validation of Array Index, as the integer overflows directly affect array indexing and memory allocation decisions. When exploited, this vulnerability can enable attackers to gain unauthorized access to graphical sessions, manipulate display output, or cause system crashes that may be exploited for further attacks. The impact is particularly severe in multi-user environments where X server processes may have elevated permissions, as the vulnerability could be leveraged to compromise the entire graphical user interface infrastructure.
Mitigation strategies for CVE-2013-1991 focus on immediate software updates and system hardening measures that align with industry best practices for managing integer overflow vulnerabilities. The primary remediation involves upgrading to libXxf86dga version 1.1.4 or later, where the integer overflow conditions have been addressed through proper input validation and boundary checking mechanisms. Organizations should implement comprehensive patch management procedures to ensure all X server implementations are updated promptly, particularly in environments where multiple users interact with graphical interfaces. Additionally, system administrators should consider implementing network segmentation and access controls to limit exposure to potentially malicious X servers, while also monitoring for unusual X server behavior that might indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation in graphics libraries and reinforces the need for rigorous security testing of system components that handle user-supplied data in privileged contexts. Security teams should also consider implementing runtime protections such as stack canaries and address space layout randomization to provide additional defense in depth against potential exploitation attempts.