CVE-2013-1981 in X.Org
Summary
by MITRE
Multiple integer overflows in X.org libX11 1.5.99.901 (1.6 RC1) and earlier allow X servers to trigger allocation of insufficient memory and a buffer overflow via vectors related to the (1) XQueryFont, (2) _XF86BigfontQueryFont, (3) XListFontsWithInfo, (4) XGetMotionEvents, (5) XListHosts, (6) XGetModifierMapping, (7) XGetPointerMapping, (8) XGetKeyboardMapping, (9) XGetWindowProperty, (10) XGetImage, (11) LoadColornameDB, (12) XrmGetFileDatabase, (13) _XimParseStringFile, or (14) TransFileName functions.
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Analysis
by VulDB Data Team • 05/14/2021
The vulnerability identified as CVE-2013-1981 represents a critical integer overflow issue affecting X.org libX11 version 1.5.99.901 and earlier releases. This flaw exists within the core X Window System client library that handles communication between X clients and X servers in Unix-like operating systems. The vulnerability stems from improper input validation in multiple font and resource management functions, creating conditions where malicious X servers can manipulate integer values to trigger memory allocation failures and subsequent buffer overflows. These functions are fundamental to X protocol operations and are frequently invoked during normal X session initialization and resource querying processes, making the attack surface particularly broad and impactful.
The technical implementation of this vulnerability involves several specific function calls that fail to properly validate integer inputs before performing memory allocations. When X servers transmit crafted data through functions such as XQueryFont, _XF86BigfontQueryFont, and XListFontsWithInfo, the libX11 library performs calculations that can result in integer overflows. These overflows cause the system to allocate insufficient memory buffers, which then become susceptible to buffer overflow conditions when the actual data exceeds the allocated space. The vulnerability affects both signed and unsigned integer operations, with the most critical impacts occurring during font database operations and resource management queries. The flaw demonstrates characteristics consistent with CWE-190, Integer Overflow or Wraparound, which specifically addresses issues where integer arithmetic results in values outside the expected range.
The operational impact of CVE-2013-1981 extends beyond simple memory corruption, as it can enable remote code execution when exploited successfully. Attackers with access to an X server can leverage these vulnerabilities to cause application crashes, memory corruption, and potentially arbitrary code execution within the context of the affected X client processes. The vulnerability is particularly dangerous in multi-user environments where X servers might be controlled by untrusted parties, as it allows for privilege escalation and system compromise. The functions affected include critical X protocol operations such as XGetWindowProperty, XGetImage, and LoadColornameDB, which are essential for rendering graphics and managing X session resources. This vulnerability directly maps to ATT&CK technique T1068, Exploitation for Privilege Escalation, and T1190, Exploit Public-Facing Application, as it represents a remote exploitation vector targeting X server communication protocols.
Mitigation strategies for CVE-2013-1981 require immediate patching of affected libX11 versions to the patched releases that address the integer overflow conditions. System administrators should prioritize updating X.org components across all affected systems, particularly those running X servers that may be exposed to untrusted clients. Additional protective measures include implementing X server access controls, restricting X11 forwarding in SSH configurations, and deploying network segmentation to limit exposure of X server services. The vulnerability highlights the importance of proper input validation and integer overflow protection in critical system libraries, as demonstrated by the CWE-190 classification that specifically addresses integer arithmetic issues. Security monitoring should focus on detecting unusual X protocol traffic patterns and memory allocation anomalies that might indicate exploitation attempts. Organizations should also consider implementing sandboxing mechanisms for X applications and establishing robust patch management processes to prevent similar vulnerabilities from being exploited in the future.